I think it's quite common for a dream to end with a bump of some sort as you wake up. I also remember hearing a while ago, that dreams, although they seem to play out in real time, are in fact extremely quick. So in the few seconds it might take for you to wake up in reaction to a noise or something, the whole dream could play out - almost like the dream is caused by the waking up suddenly, rather than being a preamble to it... I don't know if I'm explaining it very well. Also, I can't remember where I heard about it, on some TV science show I think, so I may be wrong.
And I think the tumbleweed is just you bonj, I've never dreamt of tumbleweed...