In the event of a power failure, generally your login will time out with 30 minutes of inactivity, you can simply login again using your saved email and password. 

If your session shows as still logged in, check in with your organisation admin who will be able to assess the open sessions and logout any unused sessions to allow you to login again.

If you don't have enough sessions configured in your system, please contact Support to increase this limit. This will impact billing.    

Organisation Admin

The Organisation Admin role can open All Sessions which gives them access to logging out unused sessions using the ellipsis against the session.