Logging in Gmail by a 'Hijacker'!

Read here how helpful and sensitive is the Google Accounts team! I logged in the Gmail account to find that I am not allowed for accessing it! I doubted my logging in procedure and tried logging in into it again and again twice; but failed to access my account! I thought that somebody might have hijacked my account, and hence became depressed. But here too Google offered a help for me in this. There was a message starting with 'Oops!' and a link offering the help. Through the link I was advised that I might have disabled 'Cookies' and to enable the Cookies in the Settings. I tried next this enabling of Cookies without any hope; but found it work surprisingly that I could access my account with my next logging in! I thanked God for it. What mistake could I have done? I thought about it and after a while I found it: I had cleared the Cookies by using the Clear Browsing Data after my previous logging in into my account! That played such a havoc in accessing my account!
Later on, when I checked my secondary mail inbox, I found an email from the Google Accounts team about logging in to my account by some 'hijacker,' with advice to reset the password immediately!