This phrase is American in origin and use and is rarely used outside of the nation and its people. It's used in the form of a warning, almost like the word "four" is yelled when a golf ball goes rogue. A second use is in the form of leadership - at the head of the whole organization or "heads up the whole organization." And a final popular use for the phrase is centered around emotion - when someone is down due to losing or whatever we will say "Hey, heads up - it's not over yet" or something similar. ( source )

This comes from the supposed habit of ostriches hiding when faced with attack by predators. The story was first recorded by the Roman writer Pliny the Elder, who suggested that ostriches hide their heads in bushes. Ostriches don't hide, either in bushes or sand, although they do sometimes lie on the ground to make themselves inconspicuous. The 'burying their head in the sand' myth is likely to have originated from people observing them lowering their heads when feeding. The story also relies on the supposed stupidity of ostriches, and of birds in general. In fact, there's little to support that either as birds have a significantly larger brain to weight ratio than many other species of animal. The notion is that the supposedly dumb ostrich believes that if it can't see its attacker then the attacker can't see it. This was nicely reformed as a joke on Douglas Adams' 'Hitchhiker's Guide to the Galaxy', in which the 'Ravenous Bugblatter...

The origin is the literal head over heels that can happen in a fall. Over time it morphed into a phrase that means falling in love. Read about the change over time here . 

In use since the mid-1600s, the origins of this expression are unclear beyond the obvious imagery of someone who is a bit of a fantasist (having one’s head in the clouds is clearly impossible – or at least it was in the days before aviation!). ( source )

The origin of the expression is unknown but the meaning is a loss of control over actions when you lose control of your emotions. ( source )