There is an idea in neurochemistry that the proliferation of pleasure causing neurotransmitters (i.e. dopamine) will actually decrease one's sensitivity to those neurotransmitters (because organisms tend to maintain homeostasis. There various physiological mechanisms. The presence of dopamine, for instance, probably downregulates the dopamine receptor in the post-synaptic neuron, upregulates the enzymes that break down dopamine in the synapse, and upregulates the mechanisms that re-uptake dopamine in the pre-synaptic neuron.
Supposedly, individuals suffering from bipolar disorder tend to overshoot resting levels of neurotransmitters, altrenating between manic and depressed phases.
I got zapped! I was very exited after watching my football team win, and now I am depressed for no reason.
1. When you are completely physically, emotionally, and/or mentally exhausted.
2. When you experience a sudden and extreme onset of fatigue due to a lot of stress and lack of sleep.
After getting home late from basketball practice, staying up until 3:30am to finish my homework, going to sleep and then having to wake up at 5:30am to go to school, I was completely zapped.