Sorry, but what you described isn't dehydration. If you were dehydrated then resting would not help as you would need to re hydrate to alleviate the symptoms.I've got this exaggerated reaction to really strenious exercise which tricks my brain into thinking my blood pressure is too high, which in turn signals for the blood pressure to plummet, and then I have to rest for 10-15 minutes.
Try Googling the symptoms or as mentioned earlier ask your Doctor (who I assume suggested Dehydration)?
Don't get snotty, If you also look at the replies you were given, you were told to Ask for the name of the condition we know the doc didn't initially give you one.
As for people being abrupt if you look through the various threads on here very good advice is given, sadly a lot of potential recruits come on here wanting "expert" opinion we can't do that but they are given fairly basic answers. These answers are usually given with a good reason for or against....
Get down to the AFCO see the Doc and hopefully all will be well, best case you get in. Worst case they find out whats wrong with you and it may be treatable/fixable.

