Half-staff American flag

It seems like the flag has been flying at half-staff a lot recently. I haven't been able to dig up any data on how often this has been the case, so I'm asking you all: Do you know of any reference where I can see when, for the past few years, the flag was to be flown at half-staff? I see it so often that we are either living in extremely tragic times, or the whole thing is getting trivialized. Perhaps a bit of both, or perhaps I just remember the half-staff times because they stick out in my mind, but I really don't know. Anybody got any data?