From time to time, all systems need some maintenance. Some maintenance windows require downtime, and customers are expected to be notified at least 5 days in advance. If you were surprised by a maintenance window, this article might help you.
If you have not been notified of the maintenance window, your email is probably not registered to receive those notifications. Please open a support ticket and ask to add your email.
You can also know when the maintenance starts and finishes by subscribing to the status page. After opening the link, click on subscribe and inform your email address.