Hopefully some of you out there with more medical and training experiance can diagnose this for me. A few times in the past after a couple of hours of fairly strenuous extertion, when finished I would get the following symptoms: 1st I notice my peripheral vision (especially the bottom half, and the left eye) going blurry, never affects my primary vision. 2nd I start to feel weak and what can only really be described as just "strange". 3rd I break out into cold sweats (can also include mild waves of nausea), 4th I'll get really sleepy and finally as the previous symptoms start to go away a couple hours later I'll get a mild headache.
Well, I thought I had this figured out until today as basic dehydration. However, today I went for a 12 mile ride at lunch that lasted 40 minutes and averaged 16.8 mph, nothing to hard right? It is pretty hot, about 91 and probably 80% humidity, but I'm used to it as I do this ride normally at least three days a week during lunch. I drank the same amount of water I usually do, did everything the same, and got hit by the above symptoms about 30 minutes after I got off my bike. I did eat immediatly after my ride, but again I do that every time. I can't imagine that a 40 minute ride dehydrated me to that point, but I don't know what else it could be. I do have a tendancy to hypoglycemia (low blood sugar), but this doesn't feel anything like that.
Like I said I wasn't worried about this when I thought it was dehydration after hours of working hard, and so far better managment of my water had it covered, but if a half hour ride starts to be an issue - I've got problems.
Any thoughts or ideas will be greatly appreciated.