It's not really a coma. Basically, where we last left off, he was drugged. The drugs had an effect on his mind akin to Limitless. After solving the case, due to the drugs and injuries, he was bed-ridden for a month or two. In his broken state of mind, Blackman was a persona created as a result of his mind being under attack. Look Batman RIP to get a picture of what I'm talking about