What is, overall, safer for your body: alcohol or marijuana?

I recently drank one shot of absinth(e) mixed with water at a party. I read up on it online and opinions differ vastly as to the potential for negative side effects. At this point my imagination has me suffering every possible one.

I would like to know the true possible effects and if one drink could realistically cause them. If it helps, the brand I had contained 100mg of thujone and it was Czech and I'm told they use an extract which is worse than using straight wormwood.

I hope you can help because I'm a little freaked out, the guy who gave it to me drank it extensively and recently committed suicide and I'm convinced the cause in part was the Absinthe.

My girlfriend tells me she uses marijuana to calm herself if she is having a stressful day. She has been doing this for many years. She says smoking pot is like self-medicating — it is better than using anti-depressants. She also claims smoking pot helps with depression because of how it helps produce serotonin in the body. What is serotonin and how does it help depression? Does smoking pot really help with managing your anxiety, depression, etc.?

I want to know what it is when you spontaneously trip without dropping tabs or anything. I've never had any drugs except marijuana. It is weird. I know that tripping is an induced psychosis, so am I psychotic or what? I was seeing a shrink and will be going back into treatment next semester. I think substance use is boring and a complete copout on life. I've made a lot of discoveries without needing to trip. Why does this happen? Tell me what you know.