It's taken me months to finally start to be able to frame this
question up in a way that I might get some meaningful answers.  I run
about 5 miles a day, usually 4 to 5 days a week. I'm 33, 147lbs and I
think I'm in relatively good cardio shape (resting heart rate of 43-45
if that means anything I don't know).  But when I start off my run,
today only about 6 minutes into it, and at a relatively slow pace
(probably 5.5-6 min/mile) I start to feel totally space out.  Like
just dazed.  I suppose you could call it light headed or dizzy but it
just makes me want to stop immediately.  I'm not breathing heavy at
all.  So what I usually end up doing is walking for about 5-10 minutes
and, as with today, I can start back up and actually run at a pretty
good pace for the remainder of the run with no problems at all, never
even feeling the same dizziness I feel at the beginning.  I cant
imagine its a nutrition thing anymore because of the fact that, once i
get past the dizziness, I feel great!

 I read in a biking forum
someone mention a similar thing, and one of the responses was that it
takes some time for "cardio output" to catch up with the body's need
for oxygen?  Does this make sense?  

I've been to the doctor, had blood
work and an EKG and I seem to be in very good health.

It's taken me months to finally start to be able to frame this
question up in a way that I might get some meaningful answers.  I run
about 5 miles a day, usually 4 to 5 days a week. I'm 33, 147lbs and I
think I'm in relatively good cardio shape (resting heart rate of 43-45
if that means anything I don't know).  But when I start off my run,
today only about 6 minutes into it, and at a relatively slow pace
(probably 5.5-6 min/mile) I start to feel totally space out.  Like
just dazed.  I suppose you could call it light headed or dizzy but it
just makes me want to stop immediately.  I'm not breathing heavy at
all.  So what I usually end up doing is walking for about 5-10 minutes
and, as with today, I can start back up and actually run at a pretty
good pace for the remainder of the run with no problems at all, never
even feeling the same dizziness I feel at the beginning.  I cant
imagine its a nutrition thing anymore because of the fact that, once i
get past the dizziness, I feel great!  I read in a biking forum
someone mention a similar thing, and one of the responses was that it
takes some time for "cardio output" to catch up with the body's need
for oxygen?  Does this make sense?  I've been to the doctor, had blood
work and an EKG and I seem to be in very good health.

thanks for any insight you can lend.

-john

I need to correct something.. i dont run at 5.5-6 minute miles.. i
meant 5.5-6 MPH!!!

It's taken me months to finally start to be able to frame this
question up in a way that I might get some meaningful answers. I run
about 5 miles a day, usually 4 to 5 days a week. I'm 33, 147lbs and I
think I'm in relatively good cardio shape (resting heart rate of 43-45
if that means anything I don't know). But when I start off my run,
today only about 6 minutes into it, and at a relatively slow pace
(probably 5.5-6 min/mile) I start to feel totally space out.