Aug 28th, 2012

Aha. From /var/log/messages :

Aug 28 12:38:04 norma kernel: Unable to find swap-space signature

with first appearance on August the 7th. Could this be it ?
mkswap, swapon to go back to :

Aug 28 18:48:35 norma kernel: Adding 3140696k swap on /dev/sda2.  Priority:-1 extents:1 across:3140696k