Your post saved my Corys!
Wow, am I ever grateful for the wonder of the Internet today! I recently started dosing my 6 gallon planted tank with Flourish Excel...not overdosing, just dosing. I used the recommended dosing on the bottle for a greater than 40% water change as I was changing the water today. About fifteen minutes after completing the water change, my two albino cory cats were as you said, sideways on the substrate. A panicked google search put your post first. I did as you did and changed the water again and they're back to their perky explorative selves! Phew! I know your posts fairly old so I hope you see this reply. A big thanks and another warning regarding Excel and cory cats. Incidentally, they've been just fine this week with the small maintenance dose. I will avoid the larger dose for water changes in the future for sure. Thanks again!