Left 4 Dead

This is not as hard as it looks when you first look at the achievement. What you want to do is play the game on easy with either the AI or other players. When you take damage don't use a first aid kit and rather use some pills as this will not void the achievement and will give you a temporary 30 or so HP which will go down in time. Another thing you will want to avoid is the AI's as the like to try and heal you if you under 70 or so to cancel a AI's medkit heal is to pull out the medkit you have been dragging around.

Any Questions, Just send me a message.
Gt: xGodDogx

If that's true about the going idle thing, grrrr, took me a while to figure out the perfect spot to wait out the hordes on the waiting for evac bit.

My method: Easy, No Mercy, you should easily be able to make it to the last stand on the hospital roof, but here's where I found is the best place to stand: As you come up onto the roof using the ladder, drop down to the ledge near the helipad, remember that ledge, run off and call for the helicopter, then go back to that ledge, crouch with a medipac equipped and just hold LT to melee, nothing makes it up on to the platform and you can usually take out the tank because they go for the other players, at least they did for me, repeatedly. Then when the helicopter arrives you have a very short run to make it to the level end :)

On the subject of healing while idle:

You can't take a break in single player mode, but you can take a break when you take out a second controller and play locally on splitscreen.

1) Start up a campaign on split screen and let the other controller 'take a break'.
2) Then just play the game, trying not to get hurt. The idle second controller will tag along
3) When your do get hurt and your health comes to a level that the AI tries to heal you, take control of the second controller.
4) You then can take a break with the first controller, allowing the AI to heal your idle character.
5) when the character is healed, take control of the first controller (let the second one go idle again) and play on.
6) When finishing the complete campaign, you'll get the achievement

NOTE: when I got it, I prevented my character, while in idle mode, to heal himself, I let him heal by the other AI. Don't know if it matters, but just to let you know.

This achievement is extremely easy to get.
This achievement is best got with friends.

Everytime you have a limping injury (I think it is below 40 health?) and you wish for yourself to be healed, simply press Start--->Take A Break. This will cause etheir: a) an AI to heal you, or b) you will heal yourself. When you are "idle" it will not affect this achievement at all!

disclaimer: I do not know if you can go into take a break if you are playing single player. Someone please leave a comment to improve the validity of this.

*EDIT!*
IF YOU ARE GOING TO PLAY ON SINGLE PLAYER DO AS FOLLOWS:
Load up Left 4 Dead
Select Play With Friends (x)
Select Create Lobby (x)------>Campaign
Change the settings to Easy&Campaign&Make sure it is a friend's only lobby

(Disconnect from XBL if you do not wish for your friends to join)

You may now 'Take A Break' in single player

P.S. THANKS COMMENTER!

There's the legitimate way of getting this, then there's various glitches you can use if you don't want to get it in a noble fashion.

Legit: Very, very simple achievement. Run through on Easy as fast as you can, but be careful and avoid the zombies or special infected. It's a very easy achievement to get, just don't heal. You can play with bots very easily; when they start healing you get out your medpack (so carry a medpack if you have bots playing!) and they will just stop. Pain pills are fine.

Glitch: There are several, and I'll cover them in detail.

1) Play all the way through an Easy campaign without worrying about healing; you can heal all you like! Heal heal heal! Dead Air is probably the best one to do it on. It doesn't matter at all if you get healed or heal yourself, and you can just play through without worrying about it. You have to have four human players.

Now, when you get to the finale, DO NOT open the opening saferoom door and vote to return to the lobby. Now, in 'Edit Game Settings' change it to chapter 5 (which should be the finale) and start it up again. The reason this works is because the game acknowledges the fact you've played through the whole campaign, but it says you never got incapped, never healed, and so on (so you can unlock several achievements at the same time using this). Quickly rush through to the end of the finale, where the actual finale 'event' take place. Don't heal during the finale and ding it's your's.

There is actually a glitch to beat every finale without so much as killing a single Infected. On No Mercy you can let zombies break down a door and then go into a room where the AI can't see you, on Dead Air you can jump on top of the plane by moving one or two carts with propane tanks, on Blood Harvest you can actually just stand and melee a tree and everything will immediately die before it reaches you (!) and on Death Toll there's a rock you can sit on. Crash Course, as far as I know, has no finale glitches. But I'm not going into how they work and not saying you have to use them. It has little relevance, just find them out through Google or YouTube.

I hope this helps.

Best way to do this legit is with 3 friends. Just make sure they know you are going for it as some people (such as myself) have a tendency to heal people if there are any med kits left in the safe room.

Doing this with friends allows you to basically have 4 sets of pills dedicated to one player. So whenever the person going for it gets low on health they can take their pills, and someone else can give them their set of pills.

Since that one player will not be healing you can heal your worst player twice at the beginning of every chapter.

Of course lower difficulty settings makes this easier.

Also whoever is going for the achievement should remain in the middle of the group as special infected will either go for the person in front or the person in back. Staying in the middle of the pack allows teammates to protect you from both angles.

EDIT: If you do play this with AI players you MUST keep a healthkit, or set of pain pills on you so that you can pull them out and stop AI's from healing you.

Play versus with another control, have the other control be the infected but never spawn, the player will be the only infected to spawn in the whole campaign, I got this plus 5 other achievements at the same time! Your health automatically goes back to 100 after each round so theres no need to heal

Just got this, I know I am late with it; but hey it was tough for me. I used Blood Harvest campaign, with me, my little brother, and 2 bots. I went through using only pain pills the whole way through then in the end I ran to the Farmhouse and called for rescue. Next I went upstairs and got in the kids room. I died before I got on the rescue vehicle, but my brother got in and it still gave me the achievement so even if you die you still get it.