I used to free dive for abalone a bit north of the Russian river (to avoid great whites). It wasn't very relaxing.

You're on the surface. You take a few/five deep breaths for a bit to fill your blood with extra oxygen, then flip over with your head down. You try to use as little muscle as possible in order to conserve oxygen so you do a few gentle strokes with your fins to start moving down and then no more movement. At some point the water pressure in combination with your weight belt makes it so that you start going down on your own with no effort and this accelerates the deeper you get. You just keep sinking deeper and deeper with no movement. You realize in the back of your mind that to get back to the surface you'll have expend effort to get past this equilibrium.

As you approach the bottom you scan the rocks for abalone. What you see is a black oval fringe which is the abaolones gills sticking out between its shell and the rock. When you see one you approach it with your abalone iron in your hand. If the black fringe disappears you're screwed - it means the abalone sucked itself agains the rock and you'll never get it off. If the fringe doesnt disappear you sneak up and shove the iron in between the abalone and the rock and rock it back and forth a few times to pry it off.

The abalone comes off but you fumble it almost dropping it. You clutch it to your chest and grab your gauge to measure the size. It's big enough to keep! But at this point you are completely out of oxygen. You look to the surface and see the mirror surface and waves. You kick off and begin swimming frantically with your fins to the surface. Finally breaking through, still clutching the abalone to your chest you heave breathing, spitting, and hopefully not having a bloody nose to attract sharks. You swim to your dive float and put the abalone in the bag. You look up the cliff to the road and see a natural resources officer monitoring you with binoculars.

On the dives that you don't get an abalone as you surface you try shooting a surf perch with your spear gun. Other dives you just go down and get sea urchins.

I used to give an abalone and sea urchins every few trips to my neighborhood sushi restaurant in San Francisco. Totally illegal. But I would go there with my girlfriend (now wife) on a crowded night. We'd sit at the sushi bar. He'd make us dish after dish including abalone and sake, then we'd get up and say goodbye and leave without paying. Was fun.

Oh my initial premise. Compare free diving to scuba diving. I would scuba at the same location and it was like grocery shopping. I would float up and down a giant rock face looking at the various fish hanging out and decide which one I wanted for dinner and spear it.

That said even though scuba was much easier I probably went free diving 10x as much because you didn't have to worry about all that equipment and the challenge was fun.

Do not hyperventilate, ever. Never ever. It's a miracle you survived.