You have to buy the potions before going to the 'land below' so once you use them, they are gone. So far I have only encountered 2 fairies and caught them, shortly having them revive me after I died, and finding chairs to recover hearts is hard if you do not know where to look. Heck, I passed several in the Faron Woods cause they are in the form of chopped down trees. Heart Medallions come later in the game when it gets 'tougher'.
What is even funnier, is when you are low on hearts, as we all know, Fi comes up saying "You need to replenish your health" but now she goes on to tell you that since you're in HERO mode......you are screwed and need potions.
In the Eldin province, while digging, I came across a Mogmol, getting upset with me since i 'dug above his head'. He mentions how Rupees are a common find....."....but for some reason.....Hearts don't appear anymore.....wonder why that is.."
HERO MODE BREAKS THE FOURTH WALL SO MANY TIMES!!!