So; my back tire likes to lose air. No biggie since it takes awhile. Well Due to weather and work I spent a few days on the indoor trainer, had two days off then go to get in a work out and the tire is dead flat. It had been holding air for at least two weeks. I go to pump it up and all it does is hiss. Just found it funny that it could be fine one day and have a hole in the tube two days later with no use.

There is a hole regardless, first try to see if there is still something poking a hole in the tube (or tire if it's tubeless). It could also be the valve/valve stem that's leaking air. Then either change the tube or patch the old tube if the leak is not from the valve. By the way, I'm not even sure if this is what you're asking for, or you're just stating random flat

Just wondering if anyone else has had it happen. Basically holding air for weeks then boom a hole in the tube for no reason. I've already replaced the tube. Also checked the inside of the tire to make sure it was smooth

I'm sure there's a reason for the hole. There's always a reason.

happened to me, tube was clearly defective at the seam, as it inflates it stretches leaking air in a weak spot, it deflates and closes the hole, each infation makes the weak area/hole bigger until it becomes a solid air leak and a complete flat.

There is always a reason. Could be a small fleck of pepple under the tire. could be cheap seal in the valve stem.