Relapse? Codependency?

Hello Everyone,,
Sorry I've been quiet around here for so long. Life has been super busy and the days have flown by...
Last time I posted, things seemed to have finally stabilised with my brother.
We all (family) assumed his new meds were finally kicking in...after all, it had been very rough for around 5 months.
It was so nice to have my smiling brother back again, interacting with my sons, joining us on family outings, and losing weight!
Agh, unfortunately it would seems there has been a dip in his mood again.
It's been about a month where he's been having a lot of trouble sleeping (health issues) and assume that all this lack of sleep has sent him in a downward spiral more often than not...
It's so disappointing for all of us. I find myself back where I was, a few months ago.. worrying about him most of the time subsequently, again taking my energy and focus away from my own family..

I just feel my mood drop as soon as I hear that he's low again. I become cranky around my own family and I can't seem to fully enjoy activities I should be as I'm always a bit guilty for having a nice time whilst he suffers..
I don't know how to distance myself from these more frequent ups and downs , yet not seem uncaring to him. It's draining and I'm not feeling very 'present' around my own children when I'm worrying so much!

Does anyone have any experience with a slump in effectiveness of meds? Naively I thought that once his dosage had been finally sorted, these lows were supposed to happen a lot less??!

Anyway, I do hope everyone is going ok.

Would love to hear from you

BB