Anecdotally I noticed that anti-histamine supplements for sleep cause me to have what I believe is Restless Leg Syndrome. I no longer need antihistamines to sleep. One of the reasons I gave them up was this side effect.
I didn’t think to post it until I saw a group of other people complaining about the exact same problem. There seems to be some truth to it. At this time I do not know the mechanism for action or if a nutritional supplement can counteract it.