There is a cycle to triathlon training referred to as periodization. The general model, and the one I follow, is to increase for three weeks and then to back off for one week. Then start again, a bit higher than week one of the past cycle but not quite at the week 3 level; build for three weeks and then back off again. The increase can be time or intensity, or usually a combination of both.
At the end of the training period before race day, it is time to taper. This is usually a smaller period of time for shorter races, and longer the longer the race. The common taper for the Ironman distance, and my only experience, is a 3 week taper. That’s a lot of time! Which isn’t to say that you are resting for 3 weeks at all; but because the volume is so high, you reduce it slowly(ish) over that period. For example, my long ride went from 5 hours to 3 hours to 2 hours in the 3 weeks prior to race day. And then it can depend on the sport. Swimming is easier to recover from, and I generally swim my full training distance until just about 1/2 week before race day. Whereas running I try to back off more than anything else.
This time period often comes with anxiety and energy abundance, for lack of a better word. There is nervous energy because you want to be in the best condition showing up for race day; but ideally your body is sad that it isn’t training as much as it was before and there is pent up energy wanting to get out.
For example, I just ran from the car park to the airport. Sunday I race Ironman Cozumel, so I take it as a good sign that I have the extra energy! I probably shouldn’t be running…but it wasn’t that far and we have some crazy flights so I will be sitting for a long, long time. And hopefully not getting sick. A fear of germs come with that pre-race feeling as well!