MacBook won't turn on

My MacBook suddenly turned off and was unresponsive for three days. I managed to get an appointment booked on the second day for two days later. However the evening of the third day, I thought i’d try and turn on the Mac. Voila! It turns on like it hasn’t been dead for three days. Which as fantastic as it is , being that it has recovered, but, I have learned that other apple devices of doing this and I would like to know why. As it is very disruptive considering how random and unpredictable it is.