It's very simple, one person gives you a word(s) and the person after says whatever comes to mind and on goes the same pattern.
Example:
One person says : Cat
The person after might say: Dog
It doesn't exactly have to make sense to the others; nor does your response have to be 1 word.
Also, you can NOT post after yourself - unfortunately you'll have to wait for someone else to post a reply.
And the given word is...
Insomniac