I know this thread hasn't been posted in in a few days but I just wanted to add my experience.
I need medication for multiple things and sometimes they cause mental fog at the beginning. Eventually it goes away once my body gets used to the medication. I have been able to meditate successfully while on medication.
I think that once the fog passes you should be able to meditate like you used to be able to
I also like the suggestion on starting with a small amount of time and working your way up, sounds like a great plan