Your Dr. may be the one to see about that. Getting dizzy while doing sudden movements from a stand still is one thing, but getting dizzy while sitting on a couch with no exertion is a bit concerning. However, if it was a one time thing, I personally wouldn't worry about it unless it happens again.
Heart problems that are not chronic are nearly impossible to diagnose. If a pattern develops, might want to see a cardiologist and they will strap you up with a event monitor and if it can be induced, you press a a button and it records where the problem may be.
Could be any number of other things too if it isn't your heart, and it could have been just how you were feeling that released some hormone that just dropped your pressure for the moment. Being tired or at the end of a long day could have just worn you out. If it was me, I wouldn't worry at all... but I'm not at an age where this kind of stuff is to be that concerned about as bouncing back is like nothing. If you are older, a doctor may be a good option. Or during your next check up, mention it.