What Are The Side Effects Of Tramadol?

hello im 36 years old and have had knee problems since i was 13 years old and have had 16 knee surgeries including 2 knee replacements all on my left leg.Anyway to try and make a long story short i've been on a med called tramadol for about 2 years now and everytime i stop taking it i get really sick i told my doctor this and he said that it's all in my head that tramadol is as safe as asprine his words to the dot.