I personally don't determine a healer's skill by the content they've cleared. Many players get carried to their clears. I evaluate skill by their ability to adapt to situations while optimizing their job and role. What myself and other posters are trying to express to you is it's not the difficulty of healing that is stressful. In fact, many of us welcome situations where it's heal or die because it tests our limits in clutch situations.
The impression I'm getting from you is healing comes easy to you because you don't really care about optimizing it, and/or you treat dungeons as whatever content. This is the difference between you and another healer who gets stressed. It isn't 'whatever content' to them. It is a dungeon, which requires several other RL players, and you stick out like a sore thumb when you screw up. To them, it's not that it's a dungeon; it's that it is NOT single player content, which is their comfort zone.
Healing also gets stressful when they have to carry the whole load: Tanks constantly on the verge of dying, and won't allow you to allocate MP towards DPS. DPS players with really low DPS and bad gameplay, which forces us to monitor them more, which makes monitoring the tank more stressful. An experienced healer will definitely tell you about a time or two that they felt like they carried the whole instance. Most also won't be very happy about it either and go about patting themselves on the back. That's what elitists do.
Seriously, please don't come here giving bad advice to new healers. New healers should know that if they have to spam their biggest heals to get a clear, something is seriously not right. Especially in a dungeon. You don't spam your biggest cures during big pulls either. You use your regens/shields, ogcd heals to conserve MP, and the APPROPRIATE cure depending on how much damage the tank has sustained, and how quickly it is depleting.
And I'll repeat myself. Don't be complacent.
I'm pretty sure relaxing and having fun is why most of us sub, and those who are complacent are the ones that make things more stressing than they need to be, and take some of that fun away. Make sense?