"Sori, dw i wedi blino."
Translation:Sorry, I am tired.
I can't see anything wrong with it. I will say that it sounds like an explanation, say if someone shot you a questioning look because you closed your eyes for a second, whereas the wording in the question itself sounds more like an apology. Bit more emphasis on the 'tired', bit less on the 'sorry'. That could just be how I interpret it, though.