ORIGINAL: Axel40
This has happened to me more than once and I can pretty much guarantee I didn't depress the trainer switch (although that's a pretty good guess on why it may happen.
Does make you nervous for a few flights though, just in case it happens.
I did actually lose all signal with my Spektrum once, don't know why but the plane went in but with minimal damage.
Batteries were low-ish but well before any batt alarm.
You prolly had a reboot. From what I have read on the subject it works like this. The reciever needs a certian minimal voltage to run. If your voltage dips below that amount at anytime it will reboot the reciever. The original recievers would rescan all channels before locking on to your reciever and it would take 30+ sec for it to do this. The newer versions are suposed to default back to the last known channels in case of a reboot so it only takes like 5 or so sec to perform the reboot. I only use 6volt packs in my planes to try and give an aditional buffer to keep the 2.4 revievers properly powered. Remember when your flying and your servos are working they are pulling power and can droop the voltage your pack is putting out. This meens that even though it showed low but ok on the ground once the load gets put on it might drop to unsafe levels and cause a reboot in the air.