(besides the obvious answer of "Writers have bigger priorities than taking scientific-logic into considering in their story-telling)
Imagine the Flash running from Los Angeles to New York City, 2,788 miles according to google maps. To everyone else, he does this in the blink of an eye (or faster), yet with his perceptions he seems to be moving at "normal" speeds. Let's say he's moving at a relative 70mph (we drive that fast, so his relative perceptions could still perceive everything at that (relative) pace), it would take just under 40 straight hours (in his perception) for him to complete this journey. If he was going to NYC to help with some sort of stress, it would be pretty stressful - thinking about it over & over for that long. The easy answer is that during super-speed the flashes don't have that long of a memory (such as not retaining things learned at super-speed). That to them it never feels like they've been running for more than say, 15 minutes. I'm completely fine with this answer. Like the Speed Force, I'll give it as a freebie.
However, Bart Allen has been stated to be able to retain everything during his super-speed. I would think this implies he would feel that full 40 hours. Over time, I would think this would become maddening. Another example straight from the comics - that doesn't require a thought-experiment or math, is in Teen Titans v3 when he reads an entire library. Can you imagine that? If someone told you, "Ok, start reading and don't stop. You don't have to worry about food/sleep/bathroom but you can't interact with anyone until you're done, even if you wanted to. It'll take over a year".
I would just have to imagine moments like that would eventually be maddening for Bart (especially since it's been shown he's got a short attention span (at least when younger)). Sure, it's just fiction....but this is where my mind goes.