The most common cause of unexpected CPU usage that we've seen is IPython/Jupyter notebooks. They continue to run even when you're not viewing them, and even when they're idle they "sip" CPU at a rate of about one second per minute.
You can kill all notebook-related processes from the "Consoles" page, using the processes table at the bottom of the page -- just kill anything with a name like "jupyter", "kernel" or "sudospawner". However, I don't think you'll need to do that right now if your CPU seconds used are no longer ticking up.