Triggers for Summary Fields disappeared
I had a similar experience when I cleaned out and reverted to a slightly earlier CiviCRM DB because we had made a goof (no need to elaborate on that). When I imported the desired backup, I had neither ANY triggers nor the MySQL routine civicrm_strip_non_numeric. We are running Wordpress 4.7.3 and Civi 4.7.16. I was able to recreate both the routine and the 27 triggers we use for our install by executing one of the functions for a typical site migration, namely:
{$SITE_URL}/wp-admin/admin.php?page=CiviCRM&amp;q=civicrm/menu/rebuild&amp;reset=1&amp;triggerRebuild=1 

If you're running Drupal or Joomla, there's a similar invocation. I didn't quite understand how/why it worked, but glad I stumbled across it ;). Evidently, it not only recreates triggers if missing, but adds in the missing routine. Perhaps someone with a little more experience might weigh in. I was just about to pose a question to that effect when I stumbled on your post via a search for "trigger."