There a number of different conditions and problems that can cause the legs to fall asleep, some of which are relatively minor and others that can be quite serious. Occasional numbness and tingling is often a result of reduced blood circulation. This commonly happens when one leg is crossed over the other for a long time or when a person is sitting on a hard surface without moving much, and in these cases the tingling will usually end once a person changes his or her position. More serious blood supply problems may be caused by build-up inside the veins, rather than pressure from the outside; certain medical conditions can also put undue pressure on the veins and arteries, which can lead to a feeling that the legs are “sleeping.” It’s sometimes also the case that this sort of sleep feeling can be a symptom of a larger, often unrelated ailment such as Multiple Sclerosis, or as a side effect of radiation or other cancer therapies. In general, anyone concerned about the frequency or intensity of sleeping legs is usually wise to get a medical evaluation to rule out serious conditions or issues, as well as to strategize a personalized care plan.
Blood Supply Problems
One of the most common causes for legs falling asleep is an increase in the amount of pressure placed on the nerves and veins of the body, which tends to incrementally decrease blood flow. Veins pump blood away from the limbs and extremities and towards the heart, but when they’re compressed this movement can be seriously decreased. The effect is basically the same as flattening or stepping on a hose while water is flowing out; water keeps coming, but it’s a lot slower, and the tube usually begins bulging with the mounting water pressure. In the legs this pressure often leads to numbness, especially when nerves are compressed, too.
Most often, this sort of pressure problem is temporary. A person may be sitting awkwardly, or may not be moving around enough to promote proper blood flow. In the case of crossed legs, it’s usually the case that once the upper leg is removed, sensation returns. Walking or "shaking out" the affected leg can also help to restore blood flow.
More Serious Pressure Problems
Certain medical problems could also be to blame. Enlarged blood vessels or a herniated disc can put pressure on the nerves, causing the legs to fall asleep. In some cases, scar tissue and certain infections can also increase pressure on certain veins in the body. These conditions can lead to numbness, tingling, and a feeling that the legs are falling asleep. In these situations, surgery and physical and occupational therapy are often required to ensure complete treatment.
A decrease in blood supply can also lead to legs falling asleep. Most of the time this is caused by high amounts of plaque or cholesterol in the veins, a condition known medically as atherosclerosis, and occurs most often in diabetics. In contrast, a relatively minor cause of decreased blood flow to the legs is frostbite. In most cases, once the underlying cause of the decreased blood supply is treated, the legs of the affected individual will be much less likely to fall asleep.
As a Symptom of Other Conditions
A number of serious medical conditions sometimes also include leg numbness as a symptom, and it can also be a side effect of certain medications. Patients in the early stages of Multiple Sclerosis often experience persistent numbness in the legs and feet, for instance, and it’s also somewhat common after a stroke or seizure. Radiation therapy and diets that are deficient in calcium, sodium, and potassium can also be to blame. Patients who believe they have vitamin and mineral deficiencies may want to consider using a dietary supplement. They may also want to consult with a physician or registered dietitian to get an accurate diagnosis.