Ant/Zuvai - I've been in that camp. Got a 4 minute pb at a HM on the Sunday, 20m on the Friday (where I ran a bit too fast with my new found confidence from the HM) then did a 16 or 18 on the Monday with MP miles in. My calf felt tight after the Friday run and I iced it the whole weekend then it hurt during the Monday run but still I didn't stop. In the end it cost me my Autumn marathon.
I think there were a few things going on: I definitely pushed the paces far too hard, I didn't listen to my body, I didn't look at the bigger picture, but I was also a tad unlucky.
However, I learnt a lot from that and I am more careful now following a race where I've 'gone for it'. I would expect next week to be another 50+ mileage week, mostly of easy running, but probably without the speed training on Tuesday night, although might do something later in the week. I'd still expect to do a 20m next weekend too.
I don't think its necessarily the mileage that is the risk when running on tired muscles but more the faster paces.
This year I did an off road race on the Tuesday before the GNR. Plan was to take it steady but was teamed up with three men and I ended up running the 5m loop more than 5 minutes faster than I had previously
. I had severe DOMS in the days that followed and was a bit concerned about injury at the GNR, so opted for compression socks for the first time ever. During the run my legs started off stiff but got better as I went on and actually felt a hundred times better at the end!