Wa Alaikum Essalaam wa Rahmat Allah
There was a story of this (old) man that was known to always (I mean constantly: while walking in the streets, while running errands, anytime, I guess, when we would normally be silent) say "Alhamdulillah, Astaghfir Allah." One day another man came up to him and questioned him on why he does what he does. The old man replied something along the lines of "Because we are always going from a level of high emaan to a level of low. I say Alhamdulillah for when my emaan is high and Astaghfir Allah for when my emaan is low."
(I can get you the exact story to give you a better picture inshaAllah, if you'd like.)
The point is emaan goes from a high to a low. Even the best of scholars struggled. The key is to keep up with the good habits though your heart may not be in it at the time and build yourself. What I mean is do more good - not just more of what you already do, but also do something different. You should not push yourself to following Islaam more than you can at a time, BUT you should not have a comfort level.
It's hard: I struggle with this myself and it seems like it gets a little harder each time to get that "emaan rush" back, but patience is the key as cliche as that might seem and it's well worth the struggle (as I'm sure already you know how good it feels with that feeling in your heart.) I don't know how effective this might be for you, but it helps me to be around the elderly and the very young to learn something from them about life & that somehow helps. Maybe get involved with the masjid if you aren't already and start a new program there.
Remember that you're never safe even with a high emaan so always protect it. Remember Allah in both good & not-so-good times.
This is what I tell myself; I hope it helps.
Here's something I listen to that can help inshaAllah.
http://mp3quran.net/eng/ajm_english.html
Click to listen surah 75. The Quran is a Shifaa' so listen to or read other surahs inshaAllah.