Tnanks for posting this Celeste; I'm still so very new at cycling. I went for my first 40-miler about a week ago and the ride was hilly. After the first 3 or 4 hills I had to stop just like you did, just to "catch up" and then I experienced the goosebumps and chills. I knew to stop and rest and not push it any further.
After the ride, I realized I must have been dehydrated and since I'm such a newbie I didn't/don't have the experience to judge this correctly...yet.
Anyway, the next ride I used a camelbak,(borrowed from a friend), and did much better. I also, ahem, set my own pace instead of trying to keep up with everyone else. That seems to be one of my downfalls, however it's a very steep learning curve for me and now I'm quite content to be at the back, grinding up the hills, sloowwwllly ....steadily....slooooollly.... st...ea...dily.

Jan