Like hibernation for bears and certain reptiles? That is interesting, but the difference is the lack of CO2, or does the temperature play a role as well? I must admit I don't know that much about ticks, specially their migrations habits, but this is very interesting.
It is simply a matter of waiting for food to be available. Most animals and insects only have two goals in life, eat and reproduce. Ticks get to a state where if there are no mammals nearby, they simply take a nap. There is no use for them to spend time crawling around etc if there is nothing to eat. And what wakes them up is a slight increase in carbon dioxide.. basically they smell us breathing, and that tells them a meal is nearby and they wake up.
Opportunus is confusing two different things though. A lot of diseases have a dormant phase. Many viruses enter our cells and do nothing for weeks or months. HIV is like that. A disease being dormant once it infects someone is completely different than what I am talking about.
Ticks are more like bears. They just go to sleep when there is no food around, and wake up when the food arrives.