My MIL has Dementia and has been escaping from her hospital bed (with rails) to go to the bathroom at least 3 or more times a night. Any suggestions?

This situation sounds exhausting. I will chime in on the medication. My mom was up and down throughout the night. Fell a few times. Hospice suggested melatonin a couple hours before bedtime, mirtazapine at bedtime, and lorazepam as needed if her anxiety got to the point of keeping her and everyone else awake at night. The medication timing is the key as they can cause drowsiness so be sure to discuss that with doctor. It has worked well for my mom. I hope you find something that works.

Mom must be kept awake during the day and not allowed to nap or nod off.
When she does someone has to keep waking her up. Maybe employ an aide for a couple of weeks for the daytime hours to help reset your mother's clock.
Then at night the doctor can prescribe medication for your mother. Maybe an anti-anxiety drug. Maybe even sleeping medication.
She has to be kept up during the day though.
I had lots of care clients like this who napped all day long and then were up all night. Their poor family were at their wit's end with the up all night wandering. I would not allow them to go to sleep during the day. It was hard work, but it will pay off after a few weeks.

Where is the full-time aide while mom is climbing out of bed and falling???

My mom gets into this cycle of sleeping during the day and being up all night too. I’m really not sure what sets it off but as soon as she’s up for most of one night it sets her clock off. She is often very confused about the time of day so when she asks what time it is particularly between 5 and 10 we have to remember to tell her “at night” or “in the morning”, daylight or not doesn’t always tell her and that may be part of it I think. I also know that when she takes long naps or naps after 5pm she tends to be up at night and always confused about the time. So we try to keep her up and not let her nap longer than 20-30 min during the day and particularly late afternoon. We try to keep her engaged so she won’t want to go to sleep even if it’s with the TV and better to let her nod off sitting up than lying down. It’s a drag but doing everything we can to get her up and walking engaged in something that requires her to be out of bed and off the couch during the day helps too.

If she is getting over the rails, remove them before they cause harm.
An alarm placed on the floor would alert anyone that she is trying to get out of bed.
If the aide is "full time" why is the aide not getting up when MIL gets up? Even a baby monitor would alert the aide that MIL is getting restless, then getting out of bed.
Try lowering the bed as low as it can go. That way when MIL gets her feet on the floor with the bed real low it might be more difficult for her to stand, that will slow her down a bit. Anyone coming to help her can raise the bed so it is easier for both.

I'd remove the rails since they are more a hazard than a deterrent and there is a real danger she could hurt herself badly crawling over, through, around them. Perhaps a bed assist rail and a sturdy bedside commode (the kind with a bench seat), with a floor alarm to let you know when she is up attempting to use it is the best you can do. Yes that involves waking through the night to help her but it seems you are doing that anyway?

(I hesitate to mention meds since everyone is different, but mirtazapine worked for my mom)

Ask her doctor if she can gets her meds at night so she will sleep then not all day.

….and, ummmm, she is your husband’s mother, correct? Where is he in all this? Should not be your problem at all. Make him deal with it. Not for one millisecond would I have gotten in any way involved with my mother-in-law, when she had three perfectly capable children to fool with all that. Back off! If you are the solution…well, you know the rest of that sentence.

Like Catskie62 asked below where is her "full-time" aide when your MIL is falling? And if you meant that she only has full-time help during the day, perhaps it's time she has round the clock care to help prevent future falls.
Or put a bed alarm on her bed that will alert whoever is near her that she's getting up and out of the bed.
You can't prevent falls 100% of the time, but you certainly want to do what you can to try and prevent them, as falls with the elderly can be quite harmful and even deadly.

Hospital bed rails do not prevent falls.

All facilities should know this.
Rails are no longer allowed as restraints. If a patient cannot getting out of bed safely alone, other strategies should be used eg call bells, sensor mats, floor lying bed, staff sitter. Maybe video monitoring?

Having impaired thinking really ups the dangers in hospital 😣. A bad fall can start a *cascade of adverse events*.

Unfortunately, swapping back MIL's day/night modes or reducing her need to pee overnight may be limited or not possible. But hopefully if delerium it will settle in time.

Next admission, flag this concern well with the In-Charge person & ask what strategies they will be using.

Shut that gate BEFORE the horse bolts!!

Anti anxiety medication is a suggestion, but you must understand that such medications will make your Mom more prone to falls. This is a serious and ongoing problem in all memory care and nursing home facilities. There are no restraints of any kind used any more, and I believe even the sort of confining net-beds are not used anymore.
Some things can't be fixed. If you discuss this anti anxiety medication with her doctor do ask about his experience with this increasing the chances of falling. Surely do wish you good luck.

Maybe her doctor needs to know what's going on with her meds. Where is the aide during the night?