If it's gelatin, I think you would die. Your body weight would break through the surface tension of the gelatin, so you'd go crashing to the bottom of the vat -- and there you would die of asphyxiation, because even though you were heavy enough to break through the gelatin, it would seal back up above you -- and close off your access to oxygenated air. :|
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............ sorry, I know, I'm being a spoilsport.
Now, if by "Jell-o" you meant pudding or custard, then (1) hell yeah! and (2)
http://www.youtube.com/watch?v=ed1Ucnvn08s (skip ahead to 2:10)