''Failed to login: Invalid session'' Error

Whenever I try to connect on a Minecraft Java server, I get the message: ''Failed to login: Invalid session (Try restarting your game and the launcher)''.

This issue only persists on my main account. My alt account does not show any type of problem connecting. It started a few hours ago. All tricks I have computer-wise have been used, no idea what the problem is now.

Are the servers down? Did I get hacked? Is someone else using my account?

What conclusion should I end to?