It's all common enough in people who have worked long and hard for a goal, but who have developed tunnel vision along the way. Emerging from the tunnel can be a rude shock.
That's a very true statement. I remember having a former NFL player do a speech during one of my college classes. He said after he won the super bowl he looked around and found all his team mates hitting the gym preparing for the next football season. He on the other hand institutionalized himself for suicidal thoughts. His entire purpose of the game was winning that superbowl. Unfortunately the game became his life, so when he reached that goal he felt like his life was over; he hit the summit. He later quit the game altogether when he realized that he didn't do football because he loved football, he did it for the superbowl ring. He said he played football to win the ring, while his team mates played football because they were football players.
Maybe Aikido can get a little like that for everyone every now and then? Maybe there can be this feeling of "what next, where do I go from here?" after shodan. I think when you hit that feeling you might have to do some soul searching. Figure out whether you trained for years to get that belt or if you trained because you are an Aikidoka. If you trained for the belt, maybe you should quit--you hit your summit. Aikidoka trained because that's what defines them as Aikidoka, regardless of rank.