Half of world exploded when digging (single player, infinite)

I was mining a soil block that was next to lava within a lower level (stone pickax). When I struck the soil my world exploded (Layers 65-1). Most of the blocks disappeared with a few random blocks hanging in mid-air. My chests did not disappear. I was hanging in midair with only the void (blue) under me. Most of the bedrock was gone. When I tried to move, I caught on fire and died (even though there was no lava directly around me). I respawned and was placed back up on the original place. At this point I noted that my game was 2.4 GB instead of 5+ GB. When I when I opened the door to my mine the upper layer was intact. However when I touched the door the upper layer exploded just like it did in the lower level.
Notes: I placed numerous doors throughout my mines. The explosion seemed to keep certain portions of these areas (with closed doors) intact, while almost everything else was completely gone.

Questions:
Has anyone seen this before?
Do I have to restart a new game?
Is there any way to get my game back?
Thanks.