I Have Been Getting Cramps On The Top Of Both

I have been getting cramps on the top of both feet at night. They are very painful and wake me up. It just happened again about 10 minutes ago. I have stage 3 kidney disease with high potassium so have to watch my potassium intake. What other things can cause these painful cramps and what can be done to prevent them? I do have problems with both sciaticas with nerve damage on my left leg and foot due to a bone spur pinching on the sciatica, severe arthritis on my right hip also.