To move to each side of the energy states you need to overcome a hump between. Think electron tunneling. The separated side is the lower energy state. It's just

To move to each side of the energy states you need to overcome a hump between. Think electron tunneling. The separated side is the lower energy state. It's just that we don't know a good way to 'tunnel' to that state from the higher energy state in this particular case. The separated state has an easy way to receive energy to overcome that hump. It just needs agitation. There should be a way to reverse it and gain energy but we haven't found a good way yet.