Facial cramps are making me mad! HELP!?

Well...I dont know if other people get these like me. But, sometimes I really cant control my facial expressions. Today, or really yesterday I had to voulunteer at this place with this guy who I had a pretty nice conversation with shortly before (If you know what I mean ^__~) and he kept coming closer to me and my facial muscles couldnt even make a smile and it looked like he was smitten. It made me soo mad at myself. But, I only had like 3 hours of sleep so I was sooo tired. Any tips on how to stay alert, calm and facial cramp free?