I read an article in Bottom Line Health by Mike Roizen at the Cleveland Clinic that states as long as our sleep cycles are at least 90 minutes "deep sleep" (This is the four stages of sleep leading to the REM stage) it doesnt matter if we wake several times during the night. These 90 minute sessions produce enough melatonin and growth hormone to cary us through a healthy day.
It is true we do go through sleep cycles every 90 to 120 minutes, and at times may experience micro arousals. As people mature the much needed delta sleep can decrease. Over time the micro arousals can add up to a significant sleep deficit. The body will eventually shut down and get the sleep it needs. This can even happen if you are driving, talking or working. If you find you are awakening 2 or more times a night check in with your Doctor.