Before the latest update, 2.74, I was trying to get into the nether, but my game crashed whenever I tried. So, I left it for a week (I had other things to do). When I got back, lo and behold I had spawned in the nether! On top of it! With no way down!

On the bright side, mushrooms apparently can grow on bedrock.

Another thing: apparently there's no portal either, so I truly am stuck

This is likely because of the crash you experienced in 2.73. It should not occur in 2.74 worlds.

Can you test this on a new 2.74 world and tell me if you experience the same issue? If not, I'm going to close this

That was on a 2.73 world, but the nether hadn’t been generated. I entered into a 2.74 world. In any case, I went into spectator mode and warped into the nether. In any case, the broken portal was solved by turning off shaders.