severe nausea after anal masterbation / fisting, what could it be?

i have been having anal sex for the last few years but for the last year i have started self fisting. lately i have been getting very severe nausea after anal masterbation and usually have to lay down or have a sleep as it gets that bad. because of this problem i stopped anal masterbating for a while as i thought i was doing it too often but now i can only finger myself , anything bigger and i get light headed/nausea etc.. , what could this be?

if it helps i have had no anal bleeding or stomach cramps, only nausea

this is a problem that i had a while back. in all honesty i was too afraid to go to the doctors, but i thought mine might have been down to the lubricant i used. i used ky and after a while i noticued that my anus was red and blotchy, then slowly i was only able to fit in smaller things and it got to the point where my little finger was too large. the answer for me was poppers and olive oil. poppers make your anus larger ands the olive oil actually replicates the feint smell of certain pheremones and turns on the glands in your anus to self lubricate. very soon with this method i was able to take a fist and 2 fingers from my other hand. hope this helps