I ran a 5K last Saturday--first race in 18 months, after a long struggle with hamstring injury--and did my usual 14 on Sunday. (I'm running 45 mpw.) I was a little slower than usual, but I was fine on Monday morning for my usual 3-mile jog and today I felt great.
In my experience, you can do a normal LR on the day after a 5K, but if the race is any longer than that--5 miles or more, say--you'd be better off doing a modestly reduced long run. In my case, if I'm usually running 14 (in 2:05 or so), then I'd run 10-12, or maybe even just 9, depending on how I'm feeling. That's the day after a 5 mile or 10K.
The day after a 10 miler or half marathon, just take a day off or jog an easy half hour.