X on ThinkPad crashes after sleeping (zzz'ing)

[C Thala]

Hardware: IBM ThinkPad T41
OS: FreeBSD 6.2-RELEASE-p7

My laptop recently started exhibiting very weird behavior.

Sleeping still works fine, but when I bring it back from sleep, X
Windows seems to have crashed. Whatever is on the screen (fvwm,
xscreensaver, etc.) will still be there, but there is a few lines of
weird red symbols accross the top. It will be in a frozen state, and
there is nothing I can do to get the machine to respond apart from
doing a cold boot.

Any ideas why this is happening or how to debug it?