Symptoms
In addition to the numbness in the leg, which is characteristic of a leg that has fallen asleep, other accompanying symptoms can occur. Most common is tingling in the foot or leg. When the leg wakes up again, slight pain may occur, but this disappears after a short time.
If the pressure on the affected nerves is very strong or persists for a long time, paralysis can also occur, which usually disappears after a while, depending on the extent of the nerve damage. If nerve damage occurs in the spinal region and is the cause of the leg that has fallen asleep, back pain as well as numbness and tingling may also occur in other parts of the body. In the case of a prolapsed intervertebral disc in the lumbar spine, paralysis of the foot or leg is also typical.
A leg that has fallen asleep can be a concomitant symptom of systemic diseases that can cause different symptoms throughout the body. Diabetes mellitus, for example, can cause numbness in the legs as well as symptoms such as frequent urination or severe fatigue. A leg that falls asleep during the night is usually caused by compressed nerves in the leg.
Often an unfavourable sleeping position is the cause of the symptoms described. If the legs are bent strongly or lie over the edge of the bed, for example, nerves can be compressed in such a way that the typical symptoms occur. If the complaints occur frequently, changing the mattress or trying to change the sleeping position can help prevent the legs from falling asleep.
Pain when the leg falls asleep is mainly caused by the nerves. Bending a leg, for example when sitting cross-legged, kills blood vessels and nerves. The nerves then release their neurotransmitters, which they use to send signals to the brain.
If the nerve is not completely depressed, some of these signals can still be sent to the brain. There a feeling of pain is registered. However, the pain is usually most pronounced when the leg that has fallen asleep is stretched out again. As a result, all signals can suddenly be directed to the brain, which triggers a major pain event.
Why does the leg tingle when it wakes up?
The cause of a fallen asleep leg is usually reduced blood circulation. This usually occurs when you remain in one position for a long time. Due to the lack of blood, the leg is temporarily not sufficiently supplied with oxygen and other nutrients.
For a long time, this lack of nutrients was thought to be the cause of the tingling sensation or, above all, the sudden excess of nutrients and oxygen when the leg is sufficiently supplied with blood again. The assumption was that it is mainly the muscles that are affected by pain and tingling. Only recently, researchers have come up with a new theory: It is the nerves that cause the tingling sensation.
They are trapped in positions like the cross-legged seat and are therefore easily squeezed. This leads to an increased release of the so-called neurotransmitters, i.e. the messenger substances that nerves use to send information to the brain. These neurotransmitters normally trigger an electrical potential in the nerve cell, which is passed on to the next nerve cell.
By squeezing the nerve, however, the transmitters and electrical signals cannot reach the next cell. The nerve has a break in transmission, so to speak. When the nerve is relieved again, all these signals and neurotransmitters are transmitted simultaneously, which carries a veritable firework of information to the brain.
This creates the tingling and sometimes painful feeling when the leg that has fallen asleep wakes up. The “waking” of the leg is usually completed after 30 to 60 minutes at the latest. Depending on how long the affected nerve was compressed and how high the pressure on the nerve tract was, waking up can happen very quickly or slowly.
If the symptoms do not improve after 30 to 60 minutes, a doctor should be consulted to clarify the symptoms and carry out a comprehensive diagnostic examination. This is especially true if other symptoms such as paralysis or very severe pain occur in addition to the leg that has fallen asleep. In most cases, a leg that has fallen asleep is a harmless phenomenon that can be attributed to temporary compression of one or more nerves.
In very rare cases, serious illnesses can also be behind the symptoms. If there are certain signs of a dangerous disease, it is recommended to see a doctor as soon as possible, who can make the diagnosis and initiate a therapy against the symptoms. Particularly if the symptoms persist for a long time after the leg has been moved, if there is additional pain, if the leg swells, if its skin colour changes or if there is shortness of breath, there is a risk of dangerous leg vein thrombosis. Even if there are complaints of the spinal column and paralysis symptoms occur, a physician should be consulted in order to rule out a possible herniated disc of the lumbar spine.
