What is going on in his head?

So I really Don't want the first time back in a long time to be full of my depressing thoughts, but tonight I feel like I need to vent and get feedback. So Jacob has had very good days at school up until the last week. His teacher says that he has been very angry and hitting other kids a lot. 3 in one day. I have been very concerned with the recent behavior and tonight I saw a whole other side of him. He was like a beast tonight! Allow me to paint a picture for you.

Both kids were upstairs at my mom's house watching a movie and having popcorn. (Just so you know the two of them asked to be up there) Meme has to get to early in the morning so the kids couldn't spend the night. I went up to bring them home and Julia ran down stairs before Jacob. Apparently this infuriated him because he ran to my mom's room and started slamming doors and throwing everything he could get his hands on. My mom and I both went in after him and tried to calm him down. I told him to go home and we would deal with it there. He ran passed me down stairs and jumped on top of Julia and seemed to have rage that he has never had before. He was really beating her up I had the pull him off of her and it wasn't easy. He was really trying to hurt her. Thank God he didn't, he scared her to tears but there were no bruises after the redness went away(so far) and only a few small scratches. He has never be violent like that toward her. Sure he had yelled and pushed her away but never in a really mean way not anything like this. I have never seen this in him before. I was scared.

I plan on calling a counselor in the morning to see if we can figure out what is going on with him and help him get through it. Any advise is welcome along with much needed prayer!