Without much context everything we have to go by, is guesswork. We can get close, though, who knows?
So one possibility would be "Não consigo dormir a menos que esteja/seja completamente escuro, eu (não consigo)."
I have not bumped into the expression before, but from what I have seen on the internet, my thinking is that it could be translated into "me", but then in Brazilian Portuguese something like "euzinha/euzinho/eu mesmo sim."
Just a way of speaking, to give emphasis.
Let´s wait natives or more advanced learners to chime in, though.