Gary,
Was that all of your drums or your snare drum? It sounded like all of them from the OP, but not sure.
I am going to go off on a tangent here for a minute, but bear with me. As I have mentioned in several various posts, I do tune my heads to "pitches" and those pitches are specific for each drum. The reason i do this is to keep the drums consistent at all times and any of my technicians can walk up to any of my kits, tune them and make them sound the same whether putting on new heads or touching up existing tuning. It really takes out the guess work.
The reason I mention this is you mentioned your drums sounded flat. You also mentioned that "all of them were really loose". Both of those comments are pretty subjective and perhaps not quantifiable though I do imagine you would know if the tension rods were "looser" than normal for you. In my scenario, I would simply check the drums against their known tuning and there would then be no question that the drum head had loosened or not.
Snare drums are notorious for loosening; specifically at the lugs near where you play most of your backbeats. For most of us that would be the two to four lugs near where our left stick strikes. The rim is depressed for a fraction of a second each time we play a rim shot and when that happens, the lugs can spin just a touch. After a few hundred strikes on the snare, those lugs can loosen quite a bit. A four minute song at 120bpm could easily result in 240 strikes to a snare drum so this can add up quickly. If that is the case, the standard nylon lug locks will save the day. If it is your entire kit, that just seems odd.