Now who was it that said "Keep your head down"?

I have this problem too. Somehow I just come up, and apparently a huge reason for this was a straightening of my right leg. The problem with a lot of these little habits is you will never feel or realise it, unless you are looking out for it specfically. For example if now you go and hit some balls, and only pay attention to your head level, I'm sure you can feel it coming up (now that it has already been pointed out to you by external parties).

So, all you need to do the next time you hit some balls, is simply "keep your head down" I suspect you will realise that you really have to keep note of the flex in your right leg.