Neuropathy can be a cause of extreme tiredness
An underlying problem affecting a main nerve or affecting many nerves can be a cause of tingling and numbness in the hands or arms and legs. An increased feeling of heaviness of the arms or legs or feeling tired from just holding the arms up in the air may be due to problems with the nerves rather than weakness of the muscles. Autoimmune disease or some nutrient deficiencies (vitamin B12 deficiency most common) can be causes of neuropathy, or nerve damage. Other common causes are mentioned later.
Autoimmune disease itself can be very tiring and a cause of muscle cramps and diffuse chronic pain and it could make it very hard to cope with a physically demanding job. Some types of nerve damage can become permanent but may be reversible if caught early enough and the underlying causes are corrected. Vitamin B12 may be poorly absorbed by elderly people or for others with digestive problems; a monthly injection of B12, bypassing the digestive system, is a common treatment. Dissolve in the mouth supplements of B12, cobalamin, are also used sucessfully by some people. In Parkinson's Disease neuropathy has been seen and "perhaps we should be measuring MMA levels in these patients and treating with cobalamin supplementation to reduce MMA levels and prevent neuropathy." 
Recognizing when tiredness is tiredness and when it is due to underlying nerve damage may be a step that can help prevent the nerve damage from becoming more permanent paralysis or numbness. Neuropathy can also affect gland or organ function as well as affecting motion and sensation. Poor coordination can become a problem with walking or with picking up and not dropping things because they just slipped from your fingers. Symptoms may also include feeling moments of burning or stabbing pain and bowel and bladder problems may include constipation or feeling unable to urinate. 
Neuropathy may affect approximately 24 million people in the United States. 
Neuropathy is more of a risk for people with diabetes, about 30% of the cases are associated with diabetes. Heavy alcohol use and traumatic injury can also be causes. And autoimmune celiac disease, hypothyroidism and other immune system diseases and viral infections sometimes can be a cause. Some types of antibiotics, radiation and chemotherapy treatments may cause neuropathy. Some cases of neuropathy are present at birth. 
Since celiac disease may be a cause of neuropathy trying a gluten free diet may be worth trying, (and hypothyroidism can also be a cause of neuropathy and for some people that may also be due to or made worse by gluten sensitivity problems).
Not overeating sugars and simple starches in general may help prevent neuropathy from developing by promoting more stable blood sugar. Elevated levels of blood sugar may be part of the cause of nerve damage which would be especially important for diabetics who are more at risk for elevated levels: .
Hot pepper - and it's active ingredient capsaicin may be helpful. It is available over the counter as an active ingredient in skin ointments made for pain relief for arthritis patients and others with chronic pain. Warm showers or a bath may also help circulation and muscle relaxation. Taking care with toenail health is important as numbness becomes more extreme and minor injuries may become infected and go unnoticed until they become major infections and are more visibly discolored or swollen. 
Of the 16 million Americans with diabetes, approximately, about 25% have foot problems due to peripheral neuropathy. Peripheral nerves are those extending out from the brain or spinal cord to the muscles and organs and skin. Neuropathy can progress from feeling tingling sensations of 'pins and needles' in the fingertips to not being able to feel sensations of hot, cold or pain. 
Peripheral neuropathy has been known to occur with Parkinson's disease, possibly due to treatment with L-dopa , or possibly as a side effect with another commonly used treatment, dopamine hydrochloride.  Dopamine producing cells become dysfunctional in Parkinson's Disease.  Dopamine is a brain neurostransmitter involved in movement but it is also has roles in immune system function.
Adequate levels of dopamine are involved in preventing both autoimmune disease and cancer. Research that compared the lifestyles of family members with and without Parkinson's Disease found that siblings without the disease were more likely to have been coffee drinkers (three or more cups per day) and were more likely to have smoked tobacco cigarettes. Smoking tobacco has negative health risks but it may help boost dopamine levels and may have some protective effects on the dopamine producing cells. 
Smoking tobacco may have protective effects for some people but not others due to underlying differences in genetics. Coffee intake has also been associated with less risk of developing non-alcoholic fatty liver disease (NAFLD),  but again it may be helping those with a certain type of genetics and be a negative risk for people with other types of genes. Obesity and smoking cigarettes once a patient already has non-alcoholic fatty liver disease is associated with the disease getting progressively worse.  Fructose, sugar from fruit or refined in the form of high fructose corn syrup, intake has also been associated with worsening of NAFLD.  And non-alcoholic fatty liver disease has been associated with neuropathy risk in patients with diabetes.  So protecting the liver might be helping protect the nerves at the same time.
Protecting liver function may be important for protecting against cancer. The herb milk thistle has been found to have some protective affects for the liver.  Cirrhosis of the liver is also associated with peripheral neuropathy so protecting the liver may also help protect the nervous system and brain and help prevent neuropathy from developing. 
Summary of tips for protecting against neuropathy:
Stable blood sugar and not developing diabetes may help protect the nerves.
Regular exercise and stretching and warm baths or showers and massage and other methods for increasing circulation may help protect the nerves.
Not eating excessively of fructose or simple sugars may help prevent damage caused by glycation of proteins; and by helping prevent obesity or diabetes.
Moderate use of coffee may help protect the liver from non-alcoholic fatty liver disease and some types of liver disease have been associated with peripheral neuropathy.
Dopamine or L-dopa when used as a medication to treat Parkinson's Disease may be involved in development of peripheral neuropathy. Parkinson's Disease involves dysfunctional production of dopamine so some other issue may be involved that causes peripheral neuropathy or it may be important to have adequate but not excessive levels of dopamine for health of the nerves.
A deficiency of vitamin B12, also called cobalamin, can be non-reversible cause of peripheral neuropathy. 
Smoking tobacco may have some protective affects against Parkinson's Disease for some people but it has also been associated with worsening of non-alcoholic fatty liver disease in patients who already have the disease. It is unclear at this time what genes may be involved in why some people seem less at risk from tobacco smoking than others - overall it has been found to be associated with lung cancer. Chemicals within smoke cause blood vessels to constrict and reduces circulation. It has been associated with worsening of diabetic peripheral neuropathy so quitting smoking may be more protective of nerves. While it may help boost dopamine levels there are many other healthy ways to boost dopamine naturally. 
Following a gluten free diet may be helpful in preventing peripheral neuropathy for some people. If hypothyroidism is also a problem then trying a strict gluten free diet may be beneficial as it may be a cause of autoimmune sensitivities. Eating less gluten in that case would still be exposing the body to the autoimmune 'allergen' so a trial of a gluten free diet may have to be very strict and last several months to six months before significant health benefits occur (in research on autoimmune celiac disease it took six months on a very strict gluten free diet in order for the levels of autoimmune antibodies against gluten to be reduced -- and (potentially) the thyroid hormone which the gluten molecule resembles.)
More information about dopamine and cancer and natural ways to raise dopamine levels are included in the group of Tweets mentioned in this Tweet, click to view the information on that site:
— Jennifer Depew (@deNutrients) April 7, 2017
Disclaimer: Opinions are my own and the information is provided for educational purposes within the guidelines of fair use. While I am a Registered Dietitian this information is not intended to provide individual health guidance. Please see a health professional for individual health care purposes.