Page Post Impression Count

Why do Page post impressions counts vary so wildly? I can look at my Page and see a particular post has 100 impressions. I come back a couple hours later and it has 200 then come back a couple hours later or the next day and it's down to 80.

Thanks.

Hello,

The impression count is the raw number of impressions that have been shown to users. These impressions can come from a user's news feed, a visit to the Page, or through an Open Graph social plugin.

Since many users refresh their homepage and visit their homepage multiple times during a session, and each time the post is rendered, it counts as an impression (that applies more for Page ads)

I'm sorry but that doesn't explain why the Impression count goes up and down like a toilet seat in a co-ed dorm. I understand how Impressions 'should' work. It should go in one direction - up. But it doesn't. At least not in my case. It bounces around quite significantly up, back down, back up, back down......

Thanks.