WSP Admin very slow - what more can I say?

Starting this morning, my WP Admin area has been very, very slow. I disabled all the plugins, and everything reverted to the normal lightning response I a accustomed to. I enabled the plugins one by one and after enabling WPMU DEV Dashboard everything slowed down again.

There was an update for WordPress SEO (Yoast) this morning, but I can't recall if the admin area was slow before I did the update - it was the first thing I did this morning,.