Thinking about this after reading about your knee Flossie22 (hope it's ok now) because I read your post after running 2 days in a row. I do normally have at least one rest day, although there was another recent occasion where I did a very short run the day after a more typical length one.
This time, I did the first one when I stopped off half way through a rather tedious drive - I'd seen the walk and running maps for the area and it looked a lovely place to break the journey (see picture). As time was getting on and it was off road so not lit it had to be a short run - I will allow more time there another time - and it was flat and easy running so next day, Saturday, I felt just as I would if I'd had a rest day so, after dealing with rather a lot of tricky problems, decided I would feel much better for a run so went out, had my second go at Stepping Stones and came back feeling much better for it.
Mostly the ground was a lot trickier than the day before being rather muddy, but it's a route I quite often run and I took it carefully. The distance I covered in the 2 put together was actually a bit less than I often do on a Saturday, so the total distance for the week was ok too (and I would normally do a fair amount of walking on a rest day). Does this seem ok to do now and then, or am I asking for trouble?