Yes it can cause a rare but serious syndrome that can be fatal.
depression
Hmmm... make you too happy?
depression
Overabundance of serotonin can cause serotonin syndrome.
I am assuming you are referring to the use of ecstasy (MDMA) which releases serotonin and is an SSRI (selective serotonin reuptake inhibitor). You will feel awesomely happy and empathetic with other people but if this is done too much you will become intellectually slow (e-tard). I'm not sure the mechanism of this retardation because it hasn't been extensively studied but its effects can be seen at any rave. I think it has to do with serotonin toxicity and probably at too high of levels will kill brain cells. Not sure about that though.
does Oxycodone cause serotonin syndrome
depression
Look up the effects of LSD
Not at all, being high is a nice little feeling while serotonin syndrome is a drug reaction that causes the body to have too much serotonin. Serotonin syndrome can also be life threatening.
It is too simplistic because not everyone who has too much dopamine or too little serotonin develops a disease, and because factors other than neurotransmitters influence those diseases.
This could lead to Serotonin Syndrome, where you have too much serotonin in your brain. This can lead to serious side effects, hospitalization, and even death.