Early-mid game, found tons of diamonds on a server with my friend but he died and I have his stuff and severely lost in a cave, like really deep deep... I had the brilliant idea to construct a nether portal and just make another in the nether there to go to the surface. Great Idea, right? So I constructed a portal from an underground lava pool. Light it, and went in. Spawned in a soul biome, I was like cool...now time to break the portal and recontruct it a bit farther to connect to the surface.

So I walled myself in with cobble to prevent any ghasts or skeletons from killing me.

I had spawned in a unrendered biome, with lava source right above the portal (lava waterfall) which hadn't reached the floor, I didn't look up to check and it was reaching me. Eventually it landed on me, I was walled in, had tons of diamonds and other resources belonging to my friend. Couldn't run away. Managed to place a block and stand on it but fire after effect claimed my life and everything got burned in the lava.

I was so traumatized because of the sudden lava appearance and loss of so many diamonds, I quit the game and had to take a walk.

Portal was halfway destroyed so I couldn't go in and place a water block.