Unfortunately, there is no way to answer your question. We have most of us lost geckos unexpectedly, and the way you describe his appearance is pretty much the way dead geckos look, regardless of cause. Don't be in a big hurry to blame yourself. These little ones just do up and die sometimes. Several months ago, our fearless leader and forum owner posted a lament to the unexpected loss of one of his best female breeders. A year or two ago, I lost a young adult crested gecko and one of my favorite female gargoyles for no apparent reason.
"You know, one of the hardest parts of my job is to connect Iraq to the war on terror."
President Geo. W Bush in an interview with CBS News, Washington D.C., Sept. 6, 2006