Q: My iPhone has lost all of my Calendar appointments. How can I quickly fix this awful issue???

If this is an iCloud calendar, check the calendar on icloud.com from your computer.  Do you see your calendar events there?

But did you go to icloud.com with your computer browser, sign into your account online and check your calendar there?  If so, does it still show your appointments or is it empty?

If they're gone from icloud.com, then they aren't in iCloud.  You could try waiting a while to see if this was caused by a server glitch and they will reappear.  You could also try contacting Apple support to see if there is anything they can do at their end: http://www.apple.com/support/icloud/contact/.

Otherwise, you may be able to restore them by restoring your last iCloud backup.  Doing this is a bit tricky, as you have to interrupt the restore process as soon as your phone restarts while restoring, either by putting it in airplane mode or pulling the internet connection to your router.  If you don't, iCloud will overwrite and erase any restored calendars.  Then you can disable iCloud calendar syncing and save the calendars to your phone, re-enable your wifi connection and let the restore process proceed, delete any existing calendars from icloud, and turn on icloud syncing on your phone again to upload the recover calendars to iCloud.  This process is explained in this user tip from Winston Churchill: https://discussions.apple.com/docs/DOC-4841.  While this was written for contacts, just replace calendars for contacts and for the same instructions.

Since you are having multiple problems with your icloud data being missing, you might want to start with Apple support to see what they could do for you.

If your calendar is syncing from an external account such as Hotmail it will not appear on icloud.com as it's not really an iCloud calendar.  If that's the case, open the calendar app on your phone and tap Calendars at the bottom and make sure the Hotmail calendar is checked (or tap Show All Calendars at the top) and tap Done.  If they appear now, they were just hidden from view.  If they don't, go to Settings>Mail,Contacts,Calendars...tap your Hotmail account and turn Calendars off, then back on.  Then check your calendar again to see if it appears now.

The steps in my last post were to troubleshoot your Hotmail calendars, not try to convert them to iCloud.

The first step is to make sure you haven't inadvertently turn off your Hotmail calendar from view, but going to the calendars list and making sure it's checked.  The second step is to restart calendar syncing with Hotmail.

Do you have a Hotmail account set up in Settings>Mail,Contacts,Calendars?  If so, tap it, then turn Calendars off, then back on.  This disconnects your phone from the Hotmail server, then reconnects it, which often will cure syncing problems.

It will only delete the calendar from your phone, not from the Hotmail server.  It will reappear when you turn it back on.