The nights were sleepless because there was no longer a definition of night in a ship. Night was whenever you didn't have a shift and you could turn off the lights in your quarters to pretend that the sun had gone down. Imagine that you weren't in an uncomfortable bunk, instead comfortably resting in your own bed on Caprica. Or Tauron. Scorpia. Geminon.
Felix Gaeta no longer missed the life he had, but this was because he no longer remembered it. Everything had faded into a distant dream of eternity and happiness and a life where his deepest worry was completing the combat simulations in such a flawless manner.
Felix Gaeta no longer dreamed. His dreams had grown dim and faded and even the nightmares of death at mechanical hands loosened their grip. Sleep had become an activity as professional as working in the CIC.
He thought occasionally of the time spent on New Caprica as his eyes slipped closed and wouldn't deny that waking up every morning to real sunshine was a nostalgic experience. Of course, every morning after the initial bliss of warmth on his cheeks came the dread of managing President Baltar's puppet administration. Soon the difference between real and manufactured sunlight was erased and the novelty of warmth melted away as quickly as Baltar's taste for responsibility.
This was the reason he didn't sleep anymore, because sleep implied peace. Felix did not sleep at night. Felix drifted. Felix steeped in a strong brew of his own rage and resentment and self-loathing and loathing of the people that used him to further their own means. Several names could come to mind but he let those slip away because he needed those like they needed him. He focused it instead on Baltar, clutching the name and ripping it to bloody pieces as his mind began to plateau; anger falling, rage falling, Felix falling to float on the surface.
He allowed himself to drift only until the glare of fluorescent sunlight blinded him to keep him from drowning.