Does he have his mouth open when his head is bobbing up and down? If not, then there's nothing to worry about. He's probably learning how to head bob - which is a natural beardie behavior when they're annoyed, aggravated, or just plain angry.
How fast are the head bobs? Slow, almost like he's nodding?
It's probably nothing. Gibby even head bobs at my hair sometimes. It's possible he needs more room, how big is your tank? But that's probably not why he's doing it, he probably just saw his reflection and was thinking it was another dragon.
He just did it again! (he did it when i first made this post)
and i just remembered, his BEARD (the bottom of his mount) has been all black for several days now while the rest of his body is as beautiful as a flower.
and his head "bobs" are about 1 sec apart and take about a second to go up and down. dunno if thats fast or not.
Black bearding is also normal behaviour for males, although if it's been black that long, something is seriously pissing him off (although I've never had a male going through puberty, which may be what it is). The only time Gibby's been black for that long is when I first brought Dora home, and he was pissed off at me because I wouldn't let him "get with" her.
What would happen is you'd have more dragons and more issues than you could deal with at the moment. Breeding is not a "Lets just see what happens" thing. It is a commitment that one has to be ready for.
They are solitary creatures and should be kept as such. He does not need a friend in his tank with him. That would just upset him even more.