Where do we go when we sleep?

I spend most of my days sleeping. In class, in the car, in the LRT. I can sleep almost at most just by sitting down, actually I can sleep while standing too, in the bus and in the LRT. 

And sometimes, during these times, I am completely zonked out, that sometimes I feel as if I am no longer in the classroom or in the car. 

Sometimes I wonder, where do I "go" during these times?

My professor in RELSTRI said that sometimes when we sleep we experience astral projection, which is when our souls are seperated from our bodies. And our souls get to travel in this space. So do my soul do that? Whenever I dream of someone, does that someone dream of me too. Am I visiting them? Or are they visiting me? If they are visiting me, does that mean they miss me? Or are thinking of me?

If I were to continue wasting my life in sleep, I would really like to know what happens to me during this time.