Through excessive activation of the serotonin 5-HT2B receptors, [drugs and supplement which elevate serotonin concentrations such as the selective serotonin reuptake inhibitors (SSRIs) and related antidepressants] may sometimes significantly increase blood pressure in the pulmonary artery of the heart, putting heavy strain on it as a result, thereby causing pulmonary hypertension, and may potentially even cause the often fatal cardiac fibrosis; hence, at least regarding the former, the chest pain you're experiencing. It should be noted, however, that the risk of full-blown cardiac fibrosis is considered to be substantially low, and no one has even known to have fully developed it as a result of taking an SSRI, with the notable exception of newborns in pregnant mothers taking them that is. Nonetheless, the risk is still indeed present, especially that of pulmonary hypertension; which, on the other hand, has been reported numerous times.
The anorectic agent fenfluramine (Pondimin, Fen-Phen), which is a selective serotonin releasing agent (SSRA), as well as potent 5-HT2B receptor agonist, was withdrawn from the market in 1997 because it caused numerous heart failures and killed a bunch of people, as well as required many heart transplants in those that managed to survive, on account of the effect.
Other drugs and supplements which have been prominently associated with the adverse side effect include aminorex (Menocil) and chlorphentermine (Apsedon, Desopimon, Lucofen) (both of which have been widely discontinued as a result), anything that acts as a potent and direct serotonin 5-HT2B receptor agonist (such as methysergide (Sansert) and pergolide (Permax)), and 5-HTP, as well as the illicit street drugs MDMA (Ecstasy; E, X, XTC) and its chemical relatives, and 4-methylaminorex (4-MAR, 4-MAX; Ice, EU4EUH (or Euphoria)). The SSRIs, selective-norepinephrine reuptake inhibitors (SNRIs), tricyclic antidepressants (TCAs), other serotonin reuptake inhibitors (SRIs) like sibutramine (Meridia, Reductil), and MAOIs, as well as L-tryptophan and pretty much anything that else that can significantly elevate general serotonin levels, may all cause it to a somewhat less common extent.
Don't worry though, it's fine if you get it acutely or for only a short period of time (i.e., a few weeks to months), but when you take an antidepressant or another kind of drug or supplement that significantly elevates serotonin levels chronically for a very long period of time (i.e., years) with the effect present, it can be extremely dangerous.
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By the way, for more information, see these three articles (especially the second one):
As well as these: