sometimes it helps (to slow down your mind) - by using words to tell your mind to "slow down".
When it comes to essay-writing (I used to leave mine until the weekend just before they were due, then write all weekend) - so grab a piece of paper - and start writing
down the words/ideas that come to mind - that'll get you started (as you already probably know).
Write a draft of your intro paragraph - that'll include your topic and what your essay is all about.
All the best