I have my party window closer to my other UI elements so I always have the HP and so on in view. So it doesn't happen THAT often, but I still know what you mean.

I very occasionally "zone out" in very heal-intensive situations though, few as they are, like in a big pull that drags on so long that I have to resort to Cure II spam and don't notice when there's only 1 enemy left. xD Like I could have continued to DPS a few GCDs earlier, but just kind of tunnel visioned.