Diazepam, as you well know, is a long acting benzodiazapine. Although the effects of diazepam last around 6 hours, it has many active metabolites. The half-life of diazepam itself is 20-100 hours, although in a healthy young male, it's not 100 hours. Because of the long half life, combined with the active metabolites, it stays in your system for a long time. Diazepam has the active metabolites nordiazepam, temazepam and oxazepam. Nordazepam (also called Nordiazepam and Desmethyldiazepam), although a weak benzodiazepine, is what you should take in consideration. Nordazepam has one of the longest half lifes of all benzodiazepines (36-200 hours).
Diazepam actually doesn't have as long effect as you may assume (e.g. in detox I was given diazepam 3 times a day when tapering down), it's also the metabolites that create the lingering feeling you can feel for a long time.
2.5-5 mg diazepam is a small dose. Even if you were to be physically dependent, it's not dangerous to stop cold turkey from such small doses. You will definitely experience withdrawal, but you're out of the "danger zone" with such small doses. So that's good news. If you were to be dependent, I still recommend tapering down, e.g 1 mg every 3-4 days. One important thing to follow is tolerance; if you actually feel the effect of diazepam, you are not dependent. When you're physically dependent, you don't feel the effect, it just keeps withdrawals at bay to make you feel "normal" and functional.
Benzodiazepines may help to fall to sleep and keep you sleeping, but they disturb your sleep quality. This is because there is less REM sleep when sleeping on benzos.
You haven't said how long you have taken diazepam for sleep? That would be important to know. Generally, tolerance to long acting benzos builds more slowly than short acting benzos. But because diazepam has these metabolites, they will accumulate in your system. Usually the consensus is that it takes 2-4 weeks to become physically dependent on diazepam. On the other hand, it's the best benzo of all to taper down.
There are many safer options for sleep. Have you tried melatonin? Or mirtazapine? I use melatonin and a small dose of mirtazapine for sleep, and the mirtazapine is so heavily sedating it almost knocks me out. And there's no addiction issues with small doses of mirtazapine.
Lastly; I wouldn't recommend you take diazepam for sleep for more than a couple of weeks.
Edit: Mods, why is this thead in the Pill reports section? This has nothing to do with MDMA/Ecstacy. Should the thread maybe be moved to another section?