This is most likely because of the function serotonin has on neurons and neural networks. 5ht is a g protein coupled receptor, and in the case of serotonin what

This is most likely because of the function serotonin has on neurons and neural networks. 5ht is a g protein coupled receptor, and in the case of serotonin what happens when you hit one with an agonist is you set a cascade of second messengers intracellular that modify how the cell responds, such as adjusting the protein expression of different ion channels and/or receptors. This can lead to a greatly increased sensitivity to stimuli that already exists.