Losing against lower rated opponents I play many blitz games on Lichess per day, 5 + 5 and up. When I play my A game, I can beat any 2000+ player with ease, like today. Sometimes 2200, but I don't play them much.

Anyway sometimes like what happened last week, I lost many back to back matches against various 1500, 1400 and even 1200! My rating dropped just like that to 1600, perhaps less, now I'm at 1850 looking to be back at 1900 maybe 2000 soon as I'm on a winning streak.

That's the only reason I'm not 2200 player, coz one day I might win against 2200, next day I might lose against 1200. I'm mostly play queens gambit or sicillian, no crazy oppenings.

Does that happen to all of you or is it just me? I play too many games per day, is that why this is happening to me?

I noticied that if I play one game or two, every few days I can win more high rated player with ease. I noticed that if I play many games per day I start feeling numb and anxious and stop seeing the board. is it just me or did anyone played totally rubbish after many games? 

I think I have chess addiction, if there's such thing, where I continue to play until I start losing and then play and lose more and it's so annoying.
Chess can honestly be a very tiring game since it takes a considerable amount of brain power to play. You simply play worse when you play a lot of games in a row compared to several over the course of a few days because you're just tired, it happens to everyone to a certain degree. The last thing you mentioned is called going on tilt, its a common occurrence in gaming where a lose can be demoralizing and cause you to play worse which may cause you to lose again and continue the cycle. The best way to deal with tilt is just take a break. Also if I understand you correctly you were talking about blitz chess, in my opinion blitz chess is more inconsistent compared to normal timed chess as in the time factor will give you a greater chance to beat a higher rated player compared to if you were playing normal time control chess but also a higher chance for you to lose against a lower rated opponent. I think fatigue and all those other factors I mentioned could play a part of you losing to "weaker" opponents.