Lagging after update to 19.10 from 19.04

As verified in comments the solution to lagging is to reboot into grub's Advanced Options for Ubuntu menu and select an older kernel.

Going forward try out each new kernel the system installs until one finally works properly. You can tell when a new kernel is being installed because update-initramfs and update-grub run with very unique output. Additionally you will see the new kernels on the grub Advanced Options for Ubuntu menu.

Make sure you do not autoremove the kernel that is working for you now. The only way you can autoremove it is to boot into a newer kernel and type:

sudo apt autoremove

So don't do that!

The problem is apparently caused by the swapping and disk writes in general. I found my solution by manually downgrading to kernel 5.2.21 from https://kernel.ubuntu.com/~kernel-ppa/mainline/

I'm now running it second day without problems. Micro freezes are gone and system is generally more responsive.