Why did my heart stop twice in one month?

It's not really stopping. Your heart has electrical rhythms and sometimes they can be interrupted. It's called a palpitation and it's not really dangerous unless it is frequent. Say for example your heart beat was over 100 beats per minute at rest that would be considered abnormal. Everyone has felt palpitations whether it be fast or it skipped a bit. I had one a few minutes ago which is kinda ironic that you ask about it. I haven't had one in like 3 months. It's probably happened in your sleep before and you've never noticed it. Now there are many sub categories under palpitations like Bradycardia but you don't have that. You just have what is called a flutter and that happens to most people.