Praise ye lord! My bitcoin have returned!
Thank you to everyone who replied, stopped me from having a heart attack.
Great to hear your good news.
About the sync time, it is a bit long but you seldom need to go through it again (hopefully).
About the backup, as others mentioned, the wallet has only pre-generated 100 addresses. So, please make a backup from time to time, or you may increase the number of pre-generated address using the keypool option.