Why did my iPhone delete all of my calendar entries?

Yesterday afternoon, I sync my iPhone to my computer and let it backup. All my dates were there on the phone (while it was plugged in).
This morning, I look to see why my phone hadn't alerted me for work. It turns out that all of my entries (except for birthday associated with contacts) have disappeared!
Can someone tell me what went wrong and how to get them back?

You might have checked off to replace the contacts and calendar info on your phone with the device you synced with

  • Why does iPhone automatically delete calendar events from months ago? And how do I make it stop? I use my iPhone calendar a lot and sometimes I rely on it by scrolling to previous months to see when I went for certain appts but it automatically deletes last events without asking? I know I can make special events like bdays repeat weekly or yearly but some events don't require that function, I just want to know when I went to my appts for example, what day and time it was my dentist appt. Can anyone help?
  • Why did my iphone delete all of my notes? Saying that i'm pissed off is an understatement. I want to smash the fcking thing! I had passwords and other important things saved in my notes! Why did it just get rid of everything! Can i get it back? I tried turning it off then back on hoping it was just being stupid because sometimes it does that but it comes back after i turn it off then back on.
  • Why did my iPhone delete all my contacts? I picked my iPhone 4 up to reply to a text message, and when I tried to open that message my phone froze and wouldn't open my message, phone, Bing or Google apps. I had to turn the phone off in order for the apps to open, and when they did all of my contacts were gone. What could cause this?
  • Why did my iPhone 3GS delete all my contacts? And I did not back it up on the iCloud. Is there any way I can recover them? Also, all the phone numbers are still on the Recent section, but they are all in number forms; some of them used to be on my contact list before they were wiped out, same way on my Favorites section.