If you just made level 12, buy some spells, go out and die, lose a level (back to 11)... Are you still able to cast those spells?

This has never happen to me, but I was wondering what happened? Would you simply not be able to memorize the higher level spells? Or would you be able to memorize them, just not be able to cast them? or would you be able to cast them because you have been to that level?

Thanks for any responses.

Drev