Why doesn't my depression improve when my pain does?

been logging both for a few months now and it’s messing with my head. like, you’d think better pain days = better mood, right? but that’s not what’s happening. some of my worst depression hits when my pain’s actually lower. i had a week in april where my pain was solid 4s and 5s - best stretch i’d had in ages. but my mood just tanked. couldn’t get out of bed, everything felt pointless, the whole thing. meanwhile my pain wasn’t even flaring. then other times i’m in a real flare, 7s and 8s, and my mood is weirdly… tbh fine? not happy obviously, but stable. not the crushing depression feeling. my rheum says they’re connected but separate systems, which, ok, but that doesn’t help me understand why they’re doing this. i’m starting to wonder if it’s less about pain improving and more abt the depression having its own thing going on that just happens to exist alongside the fibro. has anyone else noticed this? like your mood being independent from ur actual pain levels? i’m trying not to spiral thinking there’s something extra wrong but it’s hard not to wonder.