Thanks for responding @azygous - have a look at the video, it doesn't look like paralysis to me. It looks more like general weakness and panting (though that could of course be heat).What is your location? What has the weather been like? Hot? Beastly weather can cause this.
In chicks, sudden paralysis can also mean Marek's, though six weeks is a tad early for symptoms. A vitamin B deficiency, however, is not an uncommon cause of paralysis and leg weakness. Try the B-vitamins as @RoyalChick suggested. Make it easy on yourself and get B-complex and pop a tablet directly into the beak once a day for the next couple weeks.