Whenever you get a notification that you're suffering from minor starvation, just eat something. You can't swing a dead iguana without hitting something to eat - and even if you could, you could eat the iguana. This aspect of Hardcore mode is disappointingly un-hardcore due to the abundance of tasty food, fresh water and comfy mattresses.
In effect, your health bar is diminished from near-immortality to frighteningly finite. But Hardcore mode changes all that: now a stimpack will take several seconds so to work its magic, and in the heat of battle you're almost certainly going to take damage faster than you're healing. Those syringes full of magical juice, both the normal and super varieties, can stimulate your body from battered bones and shredded flesh back to Isaiah Mustafa -like condition in the blink of an eye, meaning that your health bar is basically infinite until you've exhausted your supply.
In normal mode, you're basically invulnerable until you run out of stimpacks. This is the biggie - all the rest of the changes combined won't affect you as much as one. More like 'HELL Yes!' 1: Stimpacks don't heal instantly
What's Hardcore mode, and are you hardcore enough to play it? Don't jump in blind: read our guide to the five big differences, and tips for how to survive the increased deadliness of the Hardcore Nevada wastes.