It took me along time to figure out that it was the keffir that was the problem. Even today I get very heavy legs from eating it, so I have dropped it in the realization that it seems to cause some sort of histamine response.
Your post might be too old to get answered, but I'll still try:
If it was a histamine reaction, wouldn't you also get it from hard cheese, aged meats (some also get histamine reactions from raw eggs)? What was your experience?
What kind of kefir did you consume (made with kefir grains, etc.)?
Did you consume raw milk? Did it affect you in any way?
Anyway, great you found relief from the symptoms.