Board Thread:Questions and Answers/@comment-26974973-20150911131111/@comment-25090680-20150911133741

Zero visited Big Boss, iirc because he was ill. He wasn't sure how long Big Boss would comatosed for, so he visited while he still could.

I don't think it's revealed when exactly BB regained consciousness. It was before Venom though, him and Ocelot talk about the plan, this wouldn't have happened before the coma. So who knows? just another loose thread.