I have not had welbutrin mixed with Paxil but have had it added to other anti-depressants that I was on at the time. It did help to some degree as the wellbutrin affects different receptors than many anti-depressants. It gave me more energy and helped me to get up in the mornings. I did not stay on it long because my doctor switched my meds and took me off the anti-depressant due to my bipolar.
Many mental health drugs will cause a flat affect. I have felt that way on several medications. They made me feel like a zombie, alive but not living. When that has happened I have let my doctor know and we have changed up medications