Blood test: they tested for serum creatinine and serum creatinine kinase level. Is that what you mean?
Medications: very occasionally, Panadol for pain relief. Also vitamin and mineral supplements. A herbal remedy "Quiet Life" that I started taking only after the cramping started. Nothing else.
Gatorade while exercising: I did try that once, and it didn't seem to make any difference. Again, my symptoms can come at any time, and don't seem to be specifically related to the time since I exercised.
Smoking and drinking: no.
So, could it be that I've picked up some virus that reduces the threshold needed for my muscles to cramp, so that now I'm less tolerant of exercise, especially one like hula hooping that I haven't done for a while?
[Added later] I think I'm seeing some patterns to the aggravating activities. There were several instances earlier on in this sequence when I went on the stationary bike in the gym, and later I was suffering with cramps, with a peak in symptoms about 48 hours later. It seems to be aggravating to work my stomach muscles: hula hooping is an extreme example. During this time, my long-standing IBS has flared up (increased cramping and gas), although (as ever) it comes and goes. The whole syndrome has been accompanied by autonomic symptoms, such as dizziness when standing up and occasional feeling of breathlessness, often just before or just after a bowel movement -- especially if the intestines are playing up.
I should say that this all started after I pulled a muscle in the thoracic back when doing a back rotarion. To address this, every day for a week in the gym I spent a short time lying on a foam roller to stretch out my back, until I eventually suspected that this was worsening my pre-existing neck sensitivity. Again, I am wondering if this in fact points towards an underlying problem at the abdomen/thoracic level. However, more or less simultaneously to the time I was healing the injury, I started feeling extremely tired for about a week and suffered several episodes of fast and weak pulse. (This seems gone now.) Could a virus (or something else) have infected a nerve in the thoracic area? Or should I be looking for some other reason for my cramping?