Strange thing involving tightening the lower back

[Axegrinder]

I was practicing my deadlift form with just the bar, and i tried tightening my lower back hard 1/3 of the way up, and for some reason this caused me to feel like i was about to feint, like when you stand up too fast and your vision fades for a minute and shit gets all tingly like blood is going places it hasnt been in awhile.. Any idea what it might have caused that?

Thanks.

[Mark Rippetoe]

No idea at all.

[bgates1654]

Vasovagal syncope

http://en.wikipedia.org/wiki/Vasovagal_syncope

Under triggers:
abdominal straining or 'bearing down' (as in defecation)

[justinbass]

Did you take a really big breath before the lift?