How To Treat Severe Fatigue During Pregnancy?

I am 10-11 weeks pregnant with third child and otherwise healthy but today when I walked from the car to the school (5mins) and then back my legs felt heavier and heavier and I walked slower and slower mincing my way along. I was really unsteady and crying as it was so weird. Felt like I would collapse at any moment. Is this anything to worry about? Not had it before