Died, respawned in lava cave

There are two problems/bugs. First, I fall through blocks when I build an "elevated rail system" that is only one block under the rail. I fall through when I jump out of the mine cart. So, I jump out and get stuck in a block and die before I can destroy the block.
Then, I get respawned somewhere in limbo, fall and die again. Then, again spawned but, this time in a lava cave somewhere under the surface. I've been stuck there for almost a day now.
I have used a fellow player in my world to try and find me and dig me out so my world that I've been working on for a while isn't a complete lose. Please help me restore my beautiful world.