That's heat exhaustion. Your body cannot get rid of the heat quick enough, thus the chill bumps. You were right to stop if you had that option. Drinking plenty of water is good and you will get better at hills (hard efforts and heat), but you always have to be very careful about this.

Not, that I'm that great at listening to my own advice. but, I remember a mountain bike race in California where it was close to 98 or so degrees and most of the climbing (long extended) was in the open - no trees. Almost everyone was quitting because of heat related issues. I was really bummed cause I was in second place (the best I had ever done to that point in my race career). I was climbing up the hill and had chill bumps on my arms and legs and kept telling myself, just go into survival mode, drink lots, and go slow, just keep going. I did that and when I hit the top of the last big hill, I was still in second place. THEN, I broke my chain! Oh, I thought I would just die! I dnf'd - just had to coast back and walk, etc. It was quite a dissappointment after I had survived that grueling race!