I was on paroxetine/Paxil for about 8-9 months, and eventually decided that I needed to get off it and move to something else because I was, um, getting so tired of being so tired, haha. I have also had experience with fluoxetine/Prozac and sertraline/Zoloft and on neither have I felt anywhere near as tired as when I was on paroxetine.
I noticed really rather as soon as I started, on just 10mg, I would yawn a ton in the early evening. At first it was good, because it helped me to get on a more regular sleeping schedule (something I struggle with) and I think just getting more rest in general helped with my overall health. But it would also annoy the people I was living with on those days that I just felt I simply could not physically get out of bed. Sometimes it was like my body was paralyzed. "Nope, you're not going to move, just go back to sleep" it would tell me.
Multiple passes on my alarm (one of those apps that makes you do all sort of math and puzzles and stuff) would barely do it. My mornings were so slow to start. I could only do something passive like watch TV for a few hours, and after two coffees would still feel like a zombie. Taking the pill earlier didn't seem to help the issue.
I actually was self-medicating for a while this way with my same old prescription (I'm in a country where the pharmacies are more lax) and even actually got a pharmacist to let me try sertraline when I convinced her that I had been tapering the paroxetine down (which I had been, because I felt like I was wasting my life just sleeping and eating meals and would never be able to hold a job like that). But I shortly thereafter went back to a psychiatrist. She actually upped my dose of sertraline. I didn't notice changes right away, but now after about 2-3 months of no more paroxetine, the change in tiredness is pretty remarkable. This past week I kept getting up early without even needing my alarm, which is craziness, haha. And I've noticed that I often don't even finish my first coffee, and haven't been making a second one. Though I suppose the renewed energy could also be an effect of the valproic acid, which she's had me on in the last month? But still, even though the paroxetine had some other very good effects, it's nice to feel that I'm not going through life half-asleep.
Of course, everybody has different experiences and side-effects, but that was my experience.