That happened a couple weeks ago for me. I shot a 36 (+1 for that course) on the front nine. Finished the back nine with a 56. It was like I forgot how to swing a golf club. Luckily my putting was on, or it could have been much worse.
10, and I did it twice. 45 on the front, 55 on the back...and then 50 on the front and 60 (!!!) on the back. I'm trying to erase that 110 round out of my mind...just was playing plain terrible. For me, anything in the 40s is acceptable...so even the 50 was a bad 9.