Ok, so
SSRI = Selective Serotonin Recapture Inhibitor
They act through the increase in the amount of extracelular Serotonin in the sinapsis by blocking the Recapture Transporter for Serotonin of the neuron that released it.
The functions of serotonin are mostly inhibitory, in the regulation of apetite, libido, sleep. And also acts in the control of anxiety, fear and the likes by intervening dopaminergic pathways.
To put you in a place most people would understand, given how its often talked about, other inhibitors of serotonin recapture would be cocaine, ecstasy, amphetamines..
you can expect the same effects from SSRI (granted, less in intensity, given how legal medications come in controlled dosis)
These medications where designed to keep you "carefree happy" is you grasp what I'm saying.
As with any anti-depressant you can expect alteration of sleep patterns, headaches, nausea.
Most secondary effects will go away after a few weeks when your organism has adapted to the medication.
This is what I can tell you purely on my theoretical knowledge
People here who have taken them will tell you that effects vary from person to person. Some even question the actual effectiveness of SSRI (in cases of mild depression or anxiety) but statistical analysis shows that they are effective for the most part and especially in cases of severe depression/anxiety
I myself only took benzodiazepines when I was a teen, and those are more on the side of dealing with stress/anxiety (heavy sleep-inducers btw) than in "keeping you happy", so I don't have much experience with your particular kind of medications other than in theory