Does being locked in chastity affect your deep sleep? During sleep men get erections 5-6 times a night. If you block a man's ability to achieve a full erection, does it likewise affect his ability to hit REM sleep?
I can say that over a span of a couple of years the device has not had a material impact on my cumulative sleep. The body adjusts. That is not to say there aren't bad nights or extra early mornings. Waking up sure that your cage is pulling your balls off. My FLR has had a far bigger impact on my sleep. I am not allowed to go to bed before my Mistress without permission and I had better not ask too often. I am always up before her as she expects me to get alot done before I wake her with her morning coffee. I almost never sleep in on weekends either as if I'm not preparing breakfast in bed for her, one of the kids has an early morning activity.
This device makes a huge difference. It prevents the chastity from pulling on your balls. I use,to hate that feeling and lose a lot of sleep. Now I sleep through the night. https://allknight.com/products/mens-wear/bdsm-mens-harness/cock-jock-cock-harness.aspx
If you have a comfortable and well fitted cage, you will will adapt. It might take weeks or a couple of months, but eventually you get there. That said, I've been wearing on and off for over 15 years, and I still get those 4am wake up calls. Getting up to pee helps relieve the pressure.
As Tom said, the key is a properly fitting device. It may take some time to get used to doing it but I have no problems sleeping caged anymore.
Have not had a problem sleeping in my jailbird from MM. Have had it for three years now. Slept through the night the first night is was on. If the sizing is right you will have no problem.