Yes, this makes sense

I came back from my long run today and felt faint even after drinking around 20 oz of water. I weighed my self and was still around 4 lbs low, so the water I drank had only made a dent. Just for the fun of it I took my blood pressure and it was really low. Something like 109/63 (I can't remember the exact figures). It sort of makes sense in that if you deplete water from the system, the blood will reflect this and be of lower volume--hence the lower pressure.

It also makes sense when you recall that one of the classes of hypertension medicines are diuretics.

I love science in action.

Update: Thu run 4.25 miles in 32:15. I feel much better now.

Update 2: The Bay State Marathon will be having water/gatoraide stations throughout the race so dehydration should not be much of a problem.

Update 3: Friday run 5.5 miles in 42:37