The longer you smoke weed the higher your tolerance to it will go up. Like you were saying it did work for pain relief but you didn't remember much else after taking it.

My theory: When you have a higher tolerance for example smoking it for about a year 5 - 6 times a day you will still get stoned but not as much as what you were the year before. So if you have a high tolerance and smoke weed for medical reasons it should still help with pain relief but you wont get as stoned as you used to.