Is it normal that i laugh quietly yet shakingly on simple things with friends?

Sometimes I tend to hide my involuntary laughs because I feel too weird to keep on laughing on some things that can make other people just smile widely at max, yet I cant help hide that I'm shaking inside out in the process. I'm 23 man and It'd just feel like a child if I just keep going on around these thoughts and laugh about it, and sometimes I laugh on just my thoughts of something funny that only might have happened around me but didn't or never happened.

I can safely add that I think I have an average sense of humor. and I think I'm a very imaginative person but probably emotional too, I'm sure that I'm NOT really "happy" when I keep on laughing about something that's not that funny and better left hidden, instead I feel uncomfortable and sometimes even mad in the process.

While i can tell this is not exactly normal for an adult, is it somewhat common in secret?

-Is there any advice on how do you keep your own short term memory refreshed and clean from certain unwanted thoughts?