There are different degrees of "Overdoses". Fatal OD's would mean, obviously, ya didn't' make it out alive.. Then you can have the luck of a non-fatal OD, involving getting revived via Narcan. In this case you'd like stop breathing for a bit, turn blue, need CPR, etc, and without help and someone to call 911 you'd likely die. Not 100%, but good chance. And there is simply taking a little too much and getting sick/passed out/etc.. What happened to you I believe was you just took a little too much, under estimated the vicious power of Methadone and the potency/half life of it, and just got a little too fucked up and passed out. While you're passed out, your body has to work extra hard to keep breathing and fundamental functions going which can account for sweating.
I just think you took too much. In my early opiate days I would take too much like that sometimes and wake up with a splitting headache, sweating, nausea, etc.
By definition, and "OD" is simply, "Taking too much". Now the degree in which you overshoot your intended dose/effect is what determines the end result. Death/Hospital/Or just dazed and confuzed 12 hrs later.
Nevertheless, the most important thing to do if you feel you are slipping too far, too fast, is CALL 911. Opiates aren't like fucking playing on the playground or some shit, it's life/death. Ideally when doing opiates having someone with you, or at least AWARE of the what you are doing and have them on standby/speed dial.
Otherwise, glad you made it out alive, taking too many opiates can be very scary/un-fun. I've seen it happen. Both with good results, and bad. Ideally we learn from the bad, as well as the good. Stay safe brotha.