SSRI (serotonin) medications like Paxil have the ability to lessen the amount of emotional significance that people attach to things. Re-read that sentence.
This is a two edged sword. It is a very helpful characteristic for people who are overwhelmed and/or very obsessive; this has helped an awful lot of people with anxiety
disorders, and OCD. The flip-side is that many people who take SSRIs for depression are not overwhelmed and do not need to be less reactive to things. However, the medication doesn't know this, and it still works the same; these people can then become apathetic and unmotivated. Often they voice being content not doing anything, not getting to work on time, not doing things they're supposed to do, because their internal prompts to get to work on time or do something they need to do becomes muted. In essence, they become too "laid-back", and to an unhelpful degree.
Paxil is not a terrible medication, but like any other tool we use to try to make lifer easier/better (stove, chainsaw, car, electricity, etc.) it can be very helpful or very hurtful.
On 80mg of Paxil daily, if he is apathetic because of the Paxil, this is not going to go away unless he reduces the dose or gets off of the Paxil. If he does reduce the dose or stop it (Please not without instructions from his doctor on how to do this), I would expect his apathy to go away.
The odd thing is that almost 100% of the time - in my experience, anyway - people generally HATE feeling numbed like this and ask what in the world is going on to make them feel that way. They don't want to keep feeling numb. Then, we talk about it and either reduce the dose or change to something else.
If it would be of help, If you want to have him ask me about this here on JustAnswer, I'd be happy to explain all this to him. All he has to do is ask a question and identify that it is meant for me, something like "Paxil question for MNPsychiatrist" or similar. Or you could simply show him our exchange.
Does this make sense?