Board Thread:Questions and Answers/@comment-26974973-20150911131111/@comment-6512-20150911133451

It's suggested he regained consciousness a few weeks or so before Venom awoke, or maybe around the same time, but it took longer for Venom to adjust. When Zero visits Big Boss, he's definitely still under (hence why Big Boss doesn't say anything, and Zero speaks to Ocelot). It's not unusual for people to visit people in hospital even if they are unconscious.