My brother commented the other day after his last Vdot test (see 'participant workout logs' on the sidebar and then TMF crew for training specifics) that although there was a huge improvement, he felt like he was really struggling - so much so that he imagined he was going quite slowly.
I learned to deal with this feeling long ago, and have pretty much been able to adjust my internal sense of 'fast and slow' as a result. The fact is that when you run twice a week (or sometimes even once) and are always pushing the intensity to some degree, you're going to end up exhausted. There are no 'easy' runs, and it turns out that my meaning of 'fast' from years of not doing any HIT (high intensity training) used to translate to 'easy'.
I am waayyyy faster than i've ever been. But because i spend all my running time in at least Zone 3 (Marathon race pace or better for those not well versed on training zones) i never really end my runs feeling good. I do end them feeling good about the run however; but because this is usually accompanied by some level of gastro-intestinal distress, severe calf tightness, and shivering (as my body struggles to regulate its body temperature after the exertion), it's not the classic endorphins and runner's high. The last few miles I always feel like i'm plodding - dragging along horribly - and wonder if i'm even managing an 8 min. mile. I feel slow.
But the training works - for me anyway - and although the time spent suffering never gets to be enjoyed by having it make something previously uncomfortable less so, it does get to be enjoyed in that for a given distance, i won't end up suffering quite as long.