Foot Pain

I spent a few hours in the electronics lab last night. I have been so weak recovering from the renal failure and CHF episode, I am just now getting to where I can do a little something around here (after over two months). It is not unusual for me to have a little foot pain from sitting for hours in there (I have always suspected it is from holding my feet at an odd angle on the circular support at the base of the drafting- style chairs at the benches in the lab).

But last night, I awakened after a couple of hours of sleep with excruciating foot pain, and what seems to be weakened knee joints as well. I am effectively crippled up to the point a trip to the bathroom is a major undertaking. Has anybody ever experienced anything like this? I have thought about electrolytes, but I should not be potassium depleted since I am on a potassium sparing diuretic. This is just horrible. Any guidance would be muchly appreciated.