I have the exact same experience when I quit coffee for any lengthy period of time. Short term withdrawal is hell, then boost of energy and the best sleep of my life consistently every night. Feel great for several weeks then realize how mundane and boring everything is without the buzz, have a cup of coffee and WOW, Im alive again! It's a brutal cycle and I fear I've done irreparable damage to my brain at this point.

As an aside, I highly recommend the Audible book "Caffeine" by Michael Pollan if you haven't already heard it. It's quite brilliant.