Contribution Level went Down?

Propably some games that You've given away went bundled because of cheap prices in RU/CIS region...

What Lemistio said ^^

Also, SG uses Steam store prices to determine CV. If store prices went down, it can drop your CV a little, too.

Atlantis 2: Beyond Atlantis, AGON - The Mysterious Codex (Trilogy) and AGON - The Lost Sword of Toledo were added to the Bundle List today - http://www.sgtools.info/lastbundled

click FAQ and scroll down to:
"What are levels, and how can I increase my level?"
for details

Its your normal cv (for now), like mine for now is 5.27 but last week was 5.46 and month before was 5.27 :)
That happend all the time, cv go up and down. If you read faq like junior said you can find some more details.