From a few comments you've made I think this is more of a reality for you than a nightmare. I'm glad you've shared it as it gives us insights into what that's like for you.
Nicely written :-) x
=^.^=

I liked how you took a pretty common (I think?) phrase and concept of "cabin fever" and re-worked it to mean so much more, trapped by your brain, body and all the questions of what could have been done. I especially liked the idea of memories humming and musical nightmares. Like they're even more alive, performing and haunting us with notes that won't give us peace of mind.

I will say I think the first half (from the first line to "that my memories hum" was the strongest part of the poem. Then, it changes to past tense which through me off and the rhyme scheme is lost. I feel like the flow would be better if you kept the rhymes, as it could smoothly speak of the nightmares of our thoughts, and if there are new nightmares when we live and wake up that we can't yet distinguish.

Or if it was your intention to transition from present tense to past, to say you conquered the darkness and found a way out, I would separate by a link break? It was interesting to read that although you escaped this particular darkness, perhaps it takes another form. To think there are multiple prisons or varying cells you can be stuck in is disheartening to say the least.

Didn't feel the need for "but" to start the lines twice in the last few verses and that last line isn't as powerful as I feel it could be? I think it would be more effective to leave it at the prison line, but describe it as something more than just a "different one". You're still stuck but the nightmare is gone in the morning, so this is a reality? Or something that comes and goes?