I had exactly the same problems for 20 years - at first only 1-2 times a year but gradually increasing to every 6 weeks. Fainting on hard bathroom floors has caused damage to a shoulder and an eye and several head gashes. I have never found a connection with any food i had eaten or any combination of foods in the previous 24 hours.
I have asked many GPs about it over the years but only got mild interest from them, and once when I got pushy I was told it could be investigated if it happened 1-2 times a week... Last year a GP gave me the label but no solution, and searching on line showed that thousands of people suffer from it and don't know what it is.
FINALLY a locum GP I went to about something else prescribed me Hyoscine Butylbromide 10mg tablets (Buscopan) and I've never looked back. You have to take two at the first sign of intestinal cramp, and they work in a couple of minutes. I haven't had an episode in 6 months, but have stopped them progressing from the cramp stage many, many times without fail. I never leave home without them now.
He did warn me that it only works if the digestive system is working, so if it has gone into stasis (eg if you have an adverse reaction to a strong antibiotic) the tablets can't be digested, so won't work. You can buy this OTC too.
Spread the word!!