laughing voices in my head?

so sometimes when I'm alone I will start to hear these voices laughing in my head! the thing is it doesn't sound like they are coming from the outside world, I know there in my head, and its really weird because I don't even hear them, I feel them laughing inside my head and they do it really fast and its impossible to describe. its really creepy and makes me really scared when its happening, like I cant move. Also, sometimes when I'm sick ( the other one that I already described happens when I'm sick too) I feel this weird thing in my imagination. it does this weird thing where its smoothens out and is sort of pleasant and then it builds up and becomes weird and ridged and is sort of scary and uncomfortable. the weird thing is I started to describe it to 2 of my friends and they heard the laughing and smooth thing too. is this normal when you are sick?