You had a heart attack. Game over.

Same thing happened to me in the middle of a field, far from civilisation.

You may find the following useful. It gave me a boost of about 15fps in major cities: http://dayzintel.com/dayz-standalone/dayz-standalone-performance-guide

If that does not work, then I would suggest waiting for a performance patch. I am doubtful that a refund is possible, but Steam support can tell you.

Post suggestions on the forums. This is a "feedback" area to report game bugs etc. Downvoted.

Just to add that I reported this issue (Only just created an account). If more information is needed, then contact me.

Duplicate of 2110, it seems.