Deadlifts for reps in the mid range always seem to get me too. It's been a while for me, but I got that feeling last session. Only two sets of 335 for 6, which is fairly easy, not crazy. Did one set, no problem. First rep on the next set felt weird, but I did another rep. Didn't do the third because I knew I was fucked. Tried to ride it out and walk out it, but nope, 3 days of walking around like a tin man. Luckily I knew to stop because it has taken me weeks to get back to normal before.
It has only happened to me twice in the last 10 years. I don't even know why it happened this time. Form was fine and I wasn't tired. Not much you can do for it once it happens.