[It took Donnie a few seconds to answer. He didn't want to make Mikey worry about him, but at the same time he needed to let it out.]

I... I-I had a nightmare... a-about something that happened... a few months ago. It happened before you got sent here... and it really scared me, and... I was worried that it was...

[That it was real... He didn't say that last part, Mikey probably got what he meant anyways.]