In Modeh Ani we thank Hashem for returning our Neshomos when we arise. Where do they go during our sleep? Do they go to the same place as the neshomos of the deceased?
The S'fas Emes certainly seems to think the n'shama spends the night in the same olam han'shamos that it came from when the person was born. This is implied in the fact that in discussing Modeh Ani, he quotes the g'mara (Nida 30b) that describes the heavens sending down the n'shama and adjuring it to be righteous and follow mitzvos before its birth into the world.
משביעין אותו תהי צדיק ואל תהי רשע
No. People lose their capacity for free will and action while asleep, and get it back in the morning.