Welcome to the forum. I am sorry your glider is now feeling well.
The problem may or may not be Hind Leg Paralysis - which is due to weakened bones. This can only be diagnosed by a vet - and usually requires X-rays to determine if the bones are weak due to calcium loss.
If your glider is not using his legs well - it might also be due to an injury. Check him to make sure he does not have any bites or cuts and gently feel his legs and back to see if he seems to be in pain. You can keep him in a bonding pouch or put him in a small cage to reduce his activity until you get to the vet if you think he has an injury.
Watch him closely this evening to see if he is eating and drinking. Hand feed him if he is not able to get to the food dish easily.
If your glider has not had fecal testing recently - that should also be done (for both gliders) to make sure there are no parasite issues. Parasites can interfere with the absorption of nutrients even if the diet has adequate calcium and the overall diet is not too high in phosphorus.
We may have some additional suggestions once you know your gliders a little better.
How old are your gliders and how long have you had them? Were they well cared for before you adopted them?
What are you currently feeding your gliders?
What fruits and vegetables do you offer?
What type of cage do you have?