I was laying in bed, and my heart skipped a beat. it did that 3 times, what can cause it to do this?

Probably is normal: Occasional skipped beats is typically normal; it is more frequently seen when you are in bed- it's quiet and not much else going on. They may be more frequent if quite fatigued or perhaps with caffeine. If a concern, a holter monitor can tell you exactly what those early beats are caused by. Most commonly would be a pac or a pvc.