How to feel old

So, a group of my college friends are turning 40, and we are taking a celebratory trip in April...to Las Vegas (I'm slightly younger, but they thought I should be included anyway). For the past six months, I've been meaning to get myself to the gym on a regular basis, and thought, hey, we haven't seen each other in years (holiday cards don't count), why don't I get a jump start and work with a trainer. I've had to cancel twice (you know, kids), and today was my first day...and I almost passed out about 10 minutes in. I mean, for real pass out--sweating, slightly nauseous, laying down on a weight bench, drinking Vitamin (sugar) Water--and enough so that the trainer didn't charge me for the session. Crap.