Recently took a week off and then on the first session back squatted 10 sets of 5 with around an 80% weight. I knew it was a bad idea, but I tend to prefer just to jump straight back in and deal with some temporary soreness rather than spend sessions working back in. In this instance it was more temporary agony than soreness.
While back I had to take two weeks off due to illness, came back and was more sensible - did upper body only. Puked. Never puked before on a day I wasn't squatting, and that's extremely rare.
Generally after a short while off I retain strength sometimes even improve, but work capacity has plummeted.