What you're describing is fairly common in all kinds of creative endeavour. It is often called post production blues or post show blues, and is well known in live music, film, theatre, etc.
Working too hard for an extended period gives you a little extra of various hormones, both adrenaline & co from the stress, and some endorphines from great things happening. When you're done and these hormone levels go down, you may suffer withdrawal symptoms (I was told at a conference a long time ago), and will feel down. If you've been running projects back to back for a long time, so you haven't had time for "getting down" between projects, you'll suffer more.
This info doesn't make the pain go away, of course, but knowing it is normal, and why it happens may help you avoid feeling there's something wrong with you. Stay strong!
Yeah. I get it. What’s the point of it all because no one cares. I’ve got three songs tracked and just can’t bring myself to jump in the lyrics. Because it’s never “good enough.” I think maybe I should just stop taking it so seriously...Finish it and be done. It’s over. Move on to the next one.
.....snip..... (emphasis added)....
I'll share this with you (and everyone else), as it has been and continues to be a helpful reminder to me in many album tracking/post-production situations.
Picasso said "A work of art is never finished; only abandoned."