What is the condition called when your heart temporarally stops in your sleep and may be fatal?

SUNDS. Sudden unexpected death syndrome, or sudden unexpected nocturnal death syndrome (sunds), is sudden unexpected death of adolescents and adults during sleep. The heart may go back into a normal rhythm thus avoiding death. Untreated sleep apnea may also cause irregularities in cardiac activity as well. An overnight sleep study or a halter monitor would yield the likely answer if you are concerned.
See Below. Likely pauses from sleep apnea or increased vagal tone (the slowing system of the central nervous system as opposed to the fast heart rate due the fight/flight system). This is usually benign unless associated with long pauses.