I do rather take issue with some parts of this post. To say that no one should speak in their sleep seems more than a little wide ranging, and to say that people with dementia (and I use the word people because I don't care for the term patients on a forum such as this) are "extremely common" and can be "easily treated" really does show a naivete about the realities of both dementia and the real world.
As to whether this is "hypomania" - maybe it is, maybe it isn't, maybe a sedative would help maybe it wouldn't. In my personal experience, administering a sedative to a person with dementia can result in a person who is now doing all the other things they were doing, but in a semi-drugged state. Now I also know people on the forum who have found that they helped. But I feel quite strongly that there is no "one solution" because, all together now - when you've seen one person with dementia you've seen one person with dementia.