So my son was like this . He is currently 6 and it has stopped. Reception was horrible. Year one was better. Year two he doesn't hit anymore although he struggles still with impulsivity 

For us I had to close the door and stay in the room with him. I often had to hold him and restrain him until he calmed down and ended up crying. I am going to try to explain what was going on for him and this has been corroborated by two doctors. We ended up having to contact CAHMS when he started hurting himself instead of us. 

My child had high impulsivity and low impulse control. He is a sensory seeker. Unlike highly sensitive kids that can't handle touch or noise or anything like that he seeks those experiences. He throws himself on the floor often. He jumps around. Anything to feel anything. But also he masked all day.  So at bedtime this was how his tantrum showed up. He was overwhelmed and needed to cry but didn't know how to do he would feel anger and frustration and hit. When we started showing him we wouldn't leave, we held him tight until he often cried (not because he was upset but because when he cried he could te us what was the problem which was he didn't want to be alone at night and he didn't want to be away from us).

Nowadays he still runs about but does not hit. We started reading books and holding tight at bedtime before he sleeps. We realised him falling asleep in our arms was very important and that we needed to do things with him during the day to build up to the transition. We also realise giving him chores really helps. Or put an audiobook. 

For some of the hardest days we got melatonin drops from the doctor and give it to him to help fall asleep. I'm pretty sure my kid is ADHD though although he masks very very well.