Pages disappeared from Google serps

[vivalasvegas]

I just noticed a 40% drop in traffic from a website I have (normally around 1000 k uniques daily). The reason: Google is no longer including my pages in its serps. The website was launched 1 year ago and until yesterday I would rank in top 5 for many searches leading to internal pages. Traffic has been steadily increasing for the past year. Even my homepage is nowhere to be found when searching for its unique title. However, when I do a site:www.mysite.com search my pages are all showing. I do not use any spammy techniques, do not even have a links page.

2 things I can think of:
1) Yesterday my host had some problems and my website would load very slow (not entirely down though).
2) Also yesterday I blocked an IP that would generate a lot of spammy looking traffic. It doesn't look like a Google IP (starts with 201.229.191)

What do you think the reason for this could be?

[ecmedia]

You may be penalized but not for the things that you mention. In any case try to unblock this IP and see what happens.

[vivalasvegas]

I just authorized the blocked IP and now I'm getting tons of hits from them again and almost none from real visitors. I said 40% drop, but the way it looks now most of my traffic is gone - Google was sending most of the clicks. It's just so scary to see this happen, especially that I can't explain it.

Some new details: when searching for a certain phrase I can sometimes find some of my pages on page 5-6 of G search results. However, these pages are barely related to the search phrase, while the page optimized for the phrase doesn't even seem to be in the serps anymore.

A correction to the first post: 1000 K uniques per day should read 1 K uniques:)