Apache server seems to fall asleep after not being used for a while

I'm having some issues with a web server. It is not used a lot yet (mainly by me now), but will be used as a live server hosting a couple hundred/thousand Wordpress sites soon.

I'm currently having the issue that when the webserver isn开发者_如何学Python't used for a bit (some minutes) it seems to 'fall asleep'. From then the first request takes an awfull long time to process and after that it runs smoothly for a bit.

The server (VPS) it's on is dedicated to being a webserver, so apache (/mysql) should be top priority. Does anybody know what I can do to improve this?

Thanks!

The issue finally solved itself when we started getting more visitors to the server, keeping it alive.