PLEASE HELP!!!!!!!!!!!!!!!?

hi, sometimes at night mainy in bed whn i go to bed, or when i wake up in middle of the night, i sometimes get this weird feeling that i have to try to over come otherwise my heart starts to beat really fast, and sometimes whn i am about to doze of i get it a little, in bed, and i used to get it in situations i didnt like e.g sunjects at school when i went like biology. sometimes i get it through the day too.