Let me preface this by saying I AM NOT A DOCTOR.    I can only tell you what _I _would look for.  FEELING you are properly hydrated can be misleading.  You may be drinking a lot, but what are you drinking??  Pop, of course is not good for hydration.  You may be drinking plenty of water, but if you are drinking lots of soda as well, the caffine will cause the water to leave your body and work against you.

The best way to tell is to (and I know this sounds gross) look at your urine.  It should be a light yellow.  Kind of like lemonade.  Don't look at it in the stool.  It will be dilluted by the water.  Urinate in a cup if you need to.  If it is darker, you are not properly hydrated.  If it is much lighter, you are over hydrated and the electrolytes have been flushed out of your body (electrolytes are what carries energy to our cells). 

IF IN DOUBT, TALK TO YOUR DOCTOR.  Your heart is kind of important for running.

Again, IF IT WERE ME (you will have to make your own decision) I would try it one more time and see what happens.  I know I am in pretty good health and I have been running before, so again, this is what I would do IF IT WERE ME!!!