Ok, now you've been really clear about the exact meaning of the full sentence, I'll still try to fiddle it so the repetition matches....just give me a sec..
on second thoughts, what I initially put in my version keeps "painful" as describing the nights:
"so painful, so painful,
feeling a tightening in my chest,
It's true I've had such nights."
I probably still like my version best
although admittedly painful is not the best word... :/
I agree with the idea of two words, but not sure which two....still think there is some hint of pain and suffering....