How to keep my father with dementia and mobility issues in bed at night?

celden: Imho, perhaps he should be seen by his physician.

I put a heated mattress pad on the bed and keep the room cool and I check on her every 2 hours

I have similar issues with my mom. She will wake up in the middle of the night and think it’s morning and get up, dress herself and come out into the living room. But she has fallen out of bed a couple times too. I have put a baby monitor on her so I can check on her and if she calls for help I will hear her, but it allows me some rest. Also I started giving her a melatonin at night to help her sleep.

If there is any possibility at all that he has the strength or inclination to try to get over, around or through bed rails I would think long and hard before using them, they are banned in facilities because of the many horrible injuries they have caused.

People have mentioned that adding a bolster of some kind below the sheet at the edge of the bed can be enough to prevent their loved one from getting up - pool noodles or rolled blankets or pillows.
Lowering the bed can make getting up more difficult, but of course it also makes it more difficult for the caregiver too unless you have an adjustable bed.
I'll add another vote for something to help him sleep through the night (along with an incontinence product if that is part of the problem).

I have a love-hate relationship when it comes to prescriptions. However, dad was not sleeping. That was causing us to lose sleep. Seroquel 50mg was the only med that got him to sleep through the night. Thinking of asking the doctor to let us try 25mg but unsure just yet because he is doing great. I just always worry about someone over-medicating once he goes to a nursing home, etc.

Bed rails did not work for us and so we had to just leave them down because he was either going over or around or between. I don't know but it did not work for us, he was escaping. One day he said all you have to do is pull that knob out and it comes down - that was a hospital bed. Sigh.

We as grandma1954 said, had one side of the bed pushed against a wall. Good luck!

If he is at home you can use bedrails.
Get a Hospital bed. Request full side rails. Or you might need 4 half rails.
When he gets into bed lower the bed as low as it will go. If you can put one side of the bed up against a wall you only have to use rails on one side.
the rails should keep him from getting up. Lowering the bed does make it more difficult for someone to get out of bed but it also makes it a lower height if they were to try to get out of bed and fell.
There are bed alarms that can be used. Either in the bed but they can go off with movement. The other option would be an alarm on the floor so if he does place his feet on the floor the alarm will go off.