By now you have heard of the Equifax fraud alert involving about 143 million people. The Federal Trade Commission has a pretty good summary on its blog of what to do in case of a credit breach. It also has a link to find out if you have potentially been impacted by this breach.
If you are part of the breach, I would at least pull a credit report and check it for suspicious activity. You may go one step further and put a fraud alert on your account by calling Equifax, Trans Union or Experian. An initial fraud alert lasts 90 days and you can remove it anytime. An extended fraud alert will last 7 years. Beyond that, you can freeze your credit which will make it inaccessible to others and also to yourself. You would have to remove it to buy a car or get a new credit card.
Further actions you can take to protect yourself after a data breach are here.
To my knowledge, this has nothing to do with your Fidelity account.