Malta,
It could be a depletion of creatine and lactic acid build-up since any muscular effort in apnea tends to cause exaggerated increases of lactate (i.e. there is not enough oxygen to permit aerobic metabolism, so your muscles rely on anaerobic metabolism). If you recovered quickly, that's probably the explanation.
There is another possible explanation involving a pressure injury. I recently suffered a mild injury from a 130' dive (which is quite deep for me) that I performed w/o sufficient warm-up. My guess is that the injury was caused by a number of factors in combination:
- the fact that peripheral blood vessels had not yet constricted (i.e. mamalian dive reflex not yet in effect)
- the fact that I was not well hydrated
- the increase in blood pressure that accompanies hypoxia
- an overly rapid ascent
After this dive, I had a dry cough, mild chest pain, could not hold my breath for more than about 30 seconds and also had a splitting headache. After researching this a little, it seems like the symptoms were very similar to a mild case of HAPE (high altitude pulmonary edema) and HACE (high altitude cerebral edema). My guess is that the increased cardiac output, overly thick blood and a rapid decrease in pressure in my peripheral body parts caused an abnormal pressure gradient across the vessels in my lungs and brain, and the result was mild edema. What is remarkable about this is that I'm reasonably certain that it was the ascent that cause the injury and not the descent adn I think that this is contrary to common wisdom about "squeeze" injuries.
The reason that I mention this is that I think that negative pressure dives could cause a similar effect and the relative pressure increase from even a modest depth like 15' is substantial. If the rubbery legs lasted for a long time, then it could be a pressure injury, and you might want to give it some time.
I am more or less recovered form my squeeze, but I intend to take a week or two off from apnea sports. I tried some statics yesterday and almost immediately had a resumption of mild symptoms (tightness in chest, dry cough etc.).