Yesterday I had chat with my host.I own www.gujaratadmission.com. This site gets 4 lac + hits in just two months. So I asked my host that whether your server able to handle the traffic or not else I will buy a dedicated server or VPS.My host owner was unable to answer and told me that can only determined if you get the traffic.So it means I can’t predicat server will go down or not ,I will get it only when it will go down and I will loose visitors.
Then I tried to google about this and got this website http://loadimpact.com/
This website tests your server by sending visitors and creating connections with server.In unregistered version you can do upto 50 users test and in registered users you can go upto 5000 users to your server.

Do this test and determine how your server will react on high huge sudden traffic.