Taking a sinemet with carbonated water gets it in fast.

The 'liquid sinemet' can be made with dilutable orange squash with vitamin C. Usually for sipping during the day, it would usually contain more sinemet, a days worth. For one night time dose make it up with not too much to drink in one go and however much sinemet for one normal nightime dose. If it is needed for more times than that you could try diluting it further and drink half at a time. Dissolve the tablet thoroughly and remember to swirl the liquid before drinking. A small plastic bottle instead of a glass might be more practical. The vit C helps it not degrade while it is sitting. As it is just for the purpose of being up briefly one dose divided is probably enough but that is something that could be adjusted. If not taking night time medication, discuss this with doctor first......

Dejibo's way to get upright is good, basically use the lower body as a counter balance to the upper, and pivot on butt as legs drop to floor. Even when very stiff this can work, especially if there is something to pull on to do the final bit of getting upright. I have a bed head with a rail, and use that to pull on.

If a commode is no use an old fashioned jug with handle, like the ones that used to come as a washstand set with a basin, could be practical. There are also lady gadgets like this that may come in handy. www.shewee.com

A friend with MS who has 'neurologic' bladder had botox for this problem, successfully, and gets it repeated every 8 months. Neuro/uro advice on whether this is appropriate could give another option.