Spawning very far away from bed, close to original spawn point

For weeks, I've been spawning just fine at my bed in my castle if I died.

Two days ago I got killed by zombies next to their monster spawner in a cave under my castle. I spawned in the air and fell to my original spawn point. Didn't worry about it just once, but every time I have died since, the same thing has happened. I have slept in my bed since then, multiple times.