In his article recapping the Nats deadline deals WaPo's Chico Harlan says that Nick Johnson was overcome by emotion when notified of his trade to Florida.
Johnson, at first, was so emotional that he knew only one response: He stayed in the cages with Eckstein and kept taking swings. But eventually, he reemerged in the clubhouse, as team employees helped him with a travel itinerary. Johnson choked back tears. He hugged teammates. In previous weeks, the Nationals had discussed a contract extension with their starting first baseman but couldn't get anything done.MLB.com's Bill Ladson, somewhat to the contrary, says that:
"Interim general manager Mike Rizzo didn't have a choice but to trade Nick Johnson because the latter did not want to negotiate an extension with the Nationals."
To my mind, there is a great difference between being unable to get a contract extension done and being unwilling to do so. If Nick was truly uninterested in extending his time in DC, I can't blame him, but that makes it harder to believe the trade came as such a terrible shock. I suppose it's possible that Johnson anticipated the trade and was nonetheless overcome by emotion in the moment. Whether his tears were of regret or relief we may never know.