do you suspect you have been a victim of phishing and your account has been hacked? though Gmail is very safe and hackers only door way to your account is user negligence and number one tool hackers use is Phising so be careful to check whether your are entering your gmail id and password in correct website link.
Recently i got email from friend with some link (Phising link) though my guess was true when i asked him he said he did not send the mail but when he logged into his gmail account and saw sent items there was more than 30 emails which he did not sent then we came to know his account was been trespassed and hacker was silently sending the mail without changing the password then we soon changed the password and all the security questions and alternate email id.
One thing came to resecue at this time was GMAIL's Login activity log which showed the hacker was connecting from one specific IP and sending mails from browser so guys it is better to check your activity log if you suspect anything fishy with your gmail.
All the gmail account Activity log can be checked by clicking details hyperlink at the end of the email web page as shown in below PIC
Now you can see a window get popped up with information such as your current ip address browser type and below that a list of previous login timings, ip address and access type such as mobile,web, pop or imap
and if your account is hacked and hacker changed your password don't worry contact Google customer support they might help you in getting your account back by investigating your account.