Strange Google indexing

Hi All,

I'm still learning the ropes of SEO.

One of my blog (about 5 months old ) stayed on the first page of google for almost a month or two for the exact domain name keyword...within few weeks of start. But then disappeared from the results for the exact domain name keyword after that initial month ( I dont check the exact SERPS position...but it wasnt in the first 5 pages0

I used to find the blog only by typing exact domainname.com.

On checking site:domain name i found all of my pages were indexed

For the last two weeks or so, i found that google put my blog on the first page for all the keyword from posts...this happened last week and i got many visits on that day as my blog was listed almost for every related keyword. (google bots kept visiting every post for every hour)

And then disappeared from the result the next day even for exact domain name keyword, now yesterday the same thing happened...google put my blog on first page and had hell lot of visitors. (Google bots kept visiting every blog post for every hour)

Today google dropped my blog. (for the exact domain name keyword)

What is happening?

Is this called google dance? What google is trying to do? Does this mean that my blog will rank again for exact domain name keyword sometime very soon.? I'm not actively building backlinks for the blog right now...do i need build more backlinks to the blog for a long lasting first SERPS?