I just woke up and my heart started to hurt when I move but then I stud up and there was no pain anymore

Hi im 12 and I just woke up and my heart started to hurt when I move but then I stud up and there was no pain anymore. I went back to sleep and then woke up an hour later feeling the same pain. I stud up again and the pain went away ! Right now I feel no pain, but what could it be or what should I do! :(