I started healing around level 30 as a druid. Burning Crusade dropped and i wanted to see what that alliance only Paladin being brought over to horde was all about. Enjoyed leveling but due to my spastic mind set, I flipped between all 3 specs. I enjoyed my self but never had over 100G due to no duel spec at the time. As I hit 70 I hit the wall of "What in the hell do I do now?" After much struggle and fruitless efforts I found a group of friends whom already had allot of heroics under there belt. I joined in as "The Backup" whatever roll we didn't have I filled. Toward the end of it I settled into healing as what i wanted to be. Now I never got into BC or Sunwell. But! I did get SSC down before the patch. We were delighted and awaited the next expansion to come out. I leveled as retribution till about 74-ish, I then tried holy out. After having the ability to AoE down 30+ mobs and heal my self I fell in love all over again. I stayed holy though out most of Wrath switching over to the other specs when my friends needed me. I never got into Ulduar as I was still in high school at the time, it was kinda suck hearing all the stories of the epic fights but I made due being a heroic all-star. Likewise with ToC, but I don't think I missed that much. Around ICC I joined in 2-3 months late but jumped in the fray as a healer with the newly attained T9 that you could get off of badges. I was able to farm quickly, being a heroic all-star after all. I only got up to Sindragosa but it was quite fun. Now rolling into the Cataclysm I started out as Holy till about 82. I was Protecbution for 83, and finished strong as Retribution. All whilst gathering gear for holy from most of my quests, only getting the other specs when there was no other option available. Sorry for this wall of text just thought I'd add a back story for the topic at hand.
My first time healing in Cataclysm was in Blackrock Caverns. It still felt very "spammy" while running, nothing I couldn't handle. Getting used to using Word of Glory in conjunction with Tower of Radiance. The healing felt different. It wasn't quite hard at all, but it was a nice change from the ability of just using one spell. I was now using two! My next stop was Stonecore. This is were the Culture Shock of healing took place. I felt helpless as my tank was taking a fairly large amount of damage and so was the group. The groups would take large AoE damage and the tank still taking a good dose of damage, as a paladin I've never been good with more than 2 people getting hit factor. Even with Light of Dawn(I dislike the spell so much.) But in the end each time I made it though almost unscathed, a few wipes from trash pulls gone bad or boss mechanics being ignored. Looking back now that I'm 85 and have a few heroics under my belt, it wasn't anything compared to the coming storm.
At 83 I stopped running dungeons and focused on the prize of 85. After reaching my goal I started into the swing of healing. Jumping into Halls of Origination the first trash pull burned almost all of my mana. I had no idea as to what in the hell happened. That tank ordered CC to be used. After words pulls only started 3/4 of my mana pool. I was confused as to what was wrong, was it my gear? I was only using Holy Light, Word of Glory, Beacon of Light, and Holy Shock. The mana coasts matched my level of mana. Everything seemed fine I only had to use flash of light once due the lack of interrupts on a shadowlancer. Keeping my cool, I didn't say a word just thought about what was wrong. Checked the tanks gear, he had a heroic helm and the rest of his gear matched up fine, the DPS was pulling along just fine. A wipe on the boss due to not understand the switch mechanics, but on our 2nd and winning attempt I ran ou of mana! I was already not used to hear the smokers voice of the Tauren, but that and it saying that I had no mana was something new. I was freaking out, racing around my head on what tricks I could pull. Thankfully the Retribution noticed my confusion and pulled out a few heals and saved the day while the boss was at 10%. It gave me enough time to gather the mana for a Divine Light on the tank to keep him from eating dirt. After words I tanked the other paladin for his quick timing and apologized for running out of mana. We continued on to finish the dungeons with no other wipes.