My drop was not that drastic but earnings went down the second half of March. Experienced a drop of about 20% in that time, clicks and ctr remained the same, only eCPM dropped. April started out really bad as well.
Whether google is up for something new and drop adsense to a minimum as a kind of market adjustment remains to be seen. Guess many are hit by these downslide and many keep it up in the hope it will improve again, - BTW there are many more million $$$ in for them by getting out this way.
I too have lost a bundle since the 'dance' back in early March. April is flat as well, don't know why since i've been online since 2000????