Sleep is a necessity for biological life, and our daily functioning.
I imagine that it could be possible to make a game whereas you will be in an underwater where little algae and fish could be swimming around, possibly some other zen environment where the environment will help you to calm down say if you’re trying to fall asleep with the help of ambience, relaxing sounds and slower moving calming relaxing visuals that move your mind to some other calming slower possibly fantasy place where you can relax and hopefully drift off to sleep.
There could be calming music or an ability to play a read story to focus on your mind on something else.
Technologically the head-set should be light and comfortable and safe to use while sleeping. There could be a reminder present that you’re in a game because you could be tricked, or disillusioned believing its reality for a moment.
It could use phase-locking technology to induce soft rocking motion for the audio. Helping to slow down the brain, subduing the brain.
Relaxing color like the color blue, essentially a virtual happy place. Perhaps rain sounds and thunder and similar visuals to help the user.
A more radical idea would be that it could also work as a virtual hub or a home of some sort. It could function as a digital notebook.
This is all but a concept, and there might already exist something like this but I deeply believe that it might be useful for those who have a hard time relaxing after work and the stresses and complexities of everyday life. Possibly help with insomnia and/or difficulty falling asleep.
Noting that, there can be many remedies and techniques you can use during your day to make it easier to fall asleep, body temperature like a warm bath or a shower, being outside in the sun, avoiding caffeine and alcohol. Having a good night routine, shutting down the lights and clearing your mind. Other ones could be working on yourself to be able to do it. Also having a happy place which you always visit or a thought that transcodes and webs out to other thoughts which can help you fall asleep too if the pattern is good.
This whole setup could also function as a sleep tracker at the same time, recording your sleep and being able to derive useful patterns from it and changing your daily habits to be able to accommodate better sleep at night.