Why do I suddenly suck?

Over the past month I have been on one of the worst downswings I have ever witnessed. A month ago I was playing super consistently and i felt like i was always the best player on the field. i managed to push all the way up to c1 div 3 which is around 1160 MMR, but then everything started going wrong. Over the past month ive lost around 300 MMr from my starting point and im now playing horribly in D1 lobbies. no matter what i do i can't seem to even acomplish basic tasks that were very easy for me just weeks ago. is this common, or is there possibly another reason for my to start randomly sucking at RL?

Update:

After I while i have clawed my way back to Champ 1 and I'm currently at 1111 MMR. def stressful but we back.