Let me further explain: The alarm you set is for waking up in the morning for going out of bed to school or whatever, but the Dream sound you set is for every REM period you have throughout the night and you have maybe about 4-8 of them. So the dream sound will be played 4-8 times during the night as you sleep in order to give you awareness in your dreams.

You should record yourself saying something like "Where are you? It's a dream, do a realitycheck"
If it accidentally wakes you up, see it as an opportunity to do a WBTB or a DEILD by practicing laying still after the sound wakes you up.