30 minutes of involuntary shaking

Today was my second session with Mark the trainer. He kicked my ass again - so much so that I had to pull over on the drive home because I was light-headed. We started with the bike (killer) and then moved on to hip flexor workout and the nautilus workout circuit. I could only do 8 reps on many of the machines. Tried to finish with the bike, but only succeeded in doing one of two reps. Mark works me at the maximum weight that I can handle on each machine. This means that on many of the exercises, my arms or legs are shaking to the point of collapse. Overall, a great workout, but I remain weak 2 hours later.