Watching the hysterics over this issue and I'm moved to observe that, while magical healing is perfectly okay to include in the game, it better not include an actual, documented physical phenomena.
SW is a thing. It's experienced most effectively by trained subjects and athletes, runners and triathletes, by martial artists and boxers, by soldiers, fire fighters. It's attributed to various biological and mental circumstances; metabolic switching / the krebs cycle, lactate shuttle / heartrate training, endorphins, or pure mental fortitude. Whatever the true cause (I'm sure different athletes and fighters get there in different ways), it's been around for years, documented in fiction and movies and studied in labs. It's a thing.
[sblock=As far as rules go, this will fall on deaf ears to those refusing to accept table-adjudication/common sense so
![Devious :] :]](http://www.enworld.org/forum/images/smilies/devious.png)
I am neither simulationist, or gamist, I am a pragmatist, I want the game to make sense, be practical, while delivering a fantastic narrative. Sometimes my stories are high-fantasy, sometimes they are low-world black-regiment dark and gritty. SW has more of a place in the black stories than the bright and heroic.
Second Wind is a phenomena that happens
during physical exertion, not at any other time. Not necessarily `combat` as a game state, but any situation wherein your hp is getting knocked down:
- straight combat
- skills combat - running a gauntlet of swinging obstacles/missles (Indi running from the boulder), 'turtling' over an innocent and taking the brunt of a continuous attack/rock fall/avalanche/cave collapse, a non-lethal combat challenge
- feats of endurance - holding up under torture, to run and continue running
This is simply using the RAW and not implying any other loophole or conflating it with other rules such as Short Rest.
To the PC that says, I rest, I SW, I rest, I SW, to 'heal'. As Mike says it's not the goal of the game to prevent that kind of play. But it IS intentionally gaming the RAW and has no place at our table (sorry, if you've ever experienced SW through physical exertion you know it doesn't work that way).
Second Wind IS NOT healing, it is a well of reserves. That some choose to treat it as such because THEIR twisted and myopic reading of the rules says so BUT, AT THE SAME TIME are railing against it because it's unrealistic, impractical or broken (see the SW+SR spam 'idea') only because that's the way THEY choose to apply it? My only response is "That's all you, baby"; THEIR choice of interpretation, THEIR choice of reaction, THEIR problem, no one else's, certainly not WotC's or the designers'. Take the childish tantrums and go. Godspeed.
Here's a gritty setting; NO magical healing, include SW + inspirational surges, Healing Kit and Potions (as combat drugs) only. That's pretty much combat. BUT that would require table-adjudication + house-ruling, but since you're reading this section I know you're okay with it that

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The idea of railing against second wind as 'non-magical healing' but being perfectly okay WITH magical healing BECAUSE you want gritty is.. well, it's 'curious' to put it kindly.