D.S.
It is totally normal. I have a 4 month old boy and he did the same thing. You might try swaddling him to help him control his arms. Also, children tend to get really spastic like that when they are overtired. You might try looking for indications that he is sleepy before he gets to this point and try and put him to sleep then. The book "Healthy Sleep Habits, Happy Baby" talks about this in detail. Good luck!