A common cop procedural trope suggests only the guilty sleep in jail. It shows up in Law and Order: SVU (S6E04), award winning movies, and even articles about poker tells. The guilty, or so the argument goes, are so relieved to be caught they accept their fate and get some rest. The innocent are so stressed by their wrongful arrest they suffer insomnia.
The tropes about a suspect's behavior extend far beyond whether or not he or she sleeps, and into the anecdotal literature around police interrogation. Psychopaths cannot empathize, thus the guilty exhibit egotism and narcissism. The "Reid [interrogation] technique" suggests innocent suspects will act angry when confronted with a false allegation (search for "Step One -- The Positive Confrontation" section, third paragraph), but warns not to read too deeply into it.
For better or worse, measuring "hours slept while in the hole" makes for messy data collection. I suspect "do only the guilty sleep in jail?" is unanswerable. The psychological state of suspects after arrest might be much easier to measure. Is there any evidence to suggest the psychological state of a suspect after arrest, but before arraignment, correlates to his or her guilt or innocence? Is there any truth to the tropes?