Massive loss of pressure in my front tire but it still holds air
A tube is a sealed system.  If the rubber isn't punctured and the valve is closed, there isn't anywhere that air could have gone all at once like that.  The only thing I can think of is maybe you do have a small blowout tire side, and somehow the tube is sitting flush against the tire in such a way that it's holding it closed for now.  May be worth taking the tire off and checking the tube itself, being prepared to replace it.  Because(in the one in a billion chance that this is what happened), if that did happen, it could be hazardous to keep riding on it.