It can be low blood pressure, restless leg syndrome, reactions to medication, dry skin, allergies, parasites, shingles and a host of others. Advice: speak with your physician and let them diagnosis, treat or refer you toward the road of recovery. Here's hoping you have better sleep soon.
There are certain people whose body reacts with itchiness whenever the brain communicates to the body that it is time to sleep. It could be a way of your body telling you when you need to go and sleep. Just in case there is another reason as to your itching, consult with your dermatologist.