ok, so about 3-4 a week i tend to fall asleep, but its a reallllly deep sleep. every single time it happens though i wake up about 5-10 minute later and i feel like i slept for years, its rather annoying and i dont understand why i do it so much? i cant seem to get to bed easily after i awake again 
what is your sleep schedule? it may have to due with lack of sleep
i get about 7-8 hours a night