At random moments i can feel my heart beating in my chest and i feel light headed and weak, but it disappears within minutes. what is it?

See your physician: The feeling of your heart beating in your chest could be palpitations. But, it shouldn't make you feel lightheaded or weak. You should see your physician - they will do an exam, likely order a heart tracing, some blood work, and maybe some other tests to make sure you are ok.

Go see a docter: Might be a heart rhythm problem or a panic attack. You need a detailed monitoring of you heart to check for rhythm issues.