Can to much Serotonin in your brain cause you to not feel emotions?

The synapse process is pretty complicated one has answered your question yet I'll give you the "Skinny."
YES. Neurotransmitters work in many ways so it would take a little research to refresh my memory as to exactly how serotonin would cause lethargy. Most of this is chemistry any way and I doubt you would be interested in that.
The amount of certain neurotransmitters can actually be measured such as dopamine in Parkinson's but you can have a normal amount of serotonin and overly sensitive receptors which would still mean you're getting to much of it. My point being that you may have an excess of serotonin but no effects what so ever.
I'm getting carried away but my answer is YES. If I am wrong I'll go back to school.