While I feel your pain, that's kinda the point of a monitoring system. It should keep contacting you until you have acknowledged it. As a "solution" I would:
1. Change your notification_period to workhours or your own window of time.
2. Change your notification_interval to something like 3-5 hours. This way, you only get a few notices that the system was down.
My Nagios system is essential to my work so I have it send me notifications every 15 minutes until I acknowledge to ensure I wake up if there is an emergency. I have never received a second one. If something is down and I didn't wake up, people start calling immediately.
