Hi, welcome to the forum, it can be restless leg syndrome or night starts (
hypnic jerks). The causes of Restless leg syndrome are peripheral neuropathies, vitamin and minerals deficiencies, lumbosacral radiculopathy, spinal stenosis, excess caffeine intake, hypoglycemia, and hypothyroidism.
He needs to undergo spinal radio imaging, blood sugar and thyroid status to rule out the cause.
Pertaining to this I suggest him to consult a neurologist to rule out the cause and treatment accordingly.