Data was deleted

For some reason OS X started to delete all my data! I do not know what happened. I looked in the console too look for any strange activity and I found "Removing observer for path: /Users/***/Pictures" along with other directories that started to get deleted. I first noticed my dropbox files started to get deleted. I thought I was hacked so I changed my passwords and was able to restore my data through dropbox site. All my keychain data is gone & app data has been deleted. Luckily I have back ups but what would cause this?