I have given up on a number of occasions, and my response varies. I generally cut down as I approach giving up, then stop.
At times I am a real arsehole, others, like this time, I am fairly good.
Still crave a bit, but that is probably because I am a first year teacher in secondary school, a very stressful job.
I was probably in my best shape in my early and mid 30's when I was commuting 30 km per day, playing 2 hours of squash a week, and training for touch footy once per week and playing two games.
Getting back into shape now, and the work for the 24 km commute I do now is probably higher than that 30 km commute because of all the hills.
And its my midlife, and I will crisis if I want to