Ok, i used to be above average in last hitting, sometimes amazing. But recently, my last hitting drops rock bottom. Anyone has any idea at all

I just got an idea: maybe it is pressure that making me bad at last hit recently. I have ADD so it takes extreme amount of focus for me to stay focus and last hit. Well, it is ranked and i under pressure to do thing well to get out of elo hell. Not to mention lots of game i have lots of asshole so it like dropping oil in fire. I actually play 4 normal games today just for fun, 2 carries and farm really well actually merely team dont have tanks so i was like meh, w/e just play for fun. (and we actually win cuz tanky dps ftw (xin and urgot tank , amazing how urgot tank 5 enemies and manage to kill 1 and drop 4 below 25% 0_o)). So, i actually decide to never play ranked again except maybe with friends cuz i actually really tired of asshole and leaver/afk/feeder. So Case Solved. Thx for u guys opinion =D