sounds like to hit the sciatic nerve a bit...
a lot of people's form with SLDLs is appaling imo, and yours might be a little off...
you really have to stick your chest out and look up - this gives you the natural arch in your back, if you let this go your asking for trouble...
far too many people arch their back the wrong way with this exercise and i squeem whenever any one does this
most people when they are doing this exercise will be no-where near the floor with their weights... ;)