My cat is scaring me! help!?

I bought this cat two days ago, and he was super sweet and gentle and he always snuggles up to me, but i'm trying to go to bed and he is running around the house acting jumpy and crazy. he's darting around like crazy, and he just came up to me, lying down, inching forward, and then pounced at me and bolted. it is reallly scaring me :( what is happening with the cat?