Sometimes twitching while you sleep can be a normal phenomenon. As a person falls deeper asleep, the parts of the brain that normally "brake" muscle activity can become deactivated; this is a normal part of the relaxation part of sleep. However, this can lead to spontaneous muscle jerks, called myoclonic jerks. Most of the time, this is not something to worry
about, as it happen to all people at some level.
However, there are also some sleep movement disorders that are distinct from myoclonic jerks. The most common of these are called restless legs syndrome
and limb movement disorder. The main thing that distinguishes normal muscle jerks during sleep from these sleep movement disorders is that the latter will result in a decreased quality of sleep. For example, people with sleep movement disorders often find that the movements or the feel of 'restlessness' in their legs either keeps them awake or wakes them up frequently after they fall asleep, resulting in significant daytime fatigue.
Your husband should consult with his primary care doctor
to make sure that he is not suffering from a sleep movement disorder. It is especially important that he consult with his doctor if he has any symptoms of trouble sleeping or feeling tired even after a sufficient period of sleep.