depression
"Let me explain how I believe Wellbutrin works, based on my experience.  When you first take it, it first has to build up in your system over a week or so.  After just a few days, you get increased energy as norepinephrine and a little bit of dopamine are increased.  This continues for about a week to a week and a half, until your brain builds up a tolerance to the neurotransmitters by increasing the number of reuptake pumps for them.  So, then you feel lethargic for another week or a little more, until the reuptake pumps finally get either overwhelmed or desensitized by the constant flood of new neurotransmitters.  Then, quite suddenly and unexpectedly, you get hit with energy again.  The energy is not euphoric but quite steady."