Felt baby...now nothing

I am just 18 weeks today and about a week ago I felt my baby kick for the first time! Before that I felt the purrs and flutters pretty consistently. After my first time feeling the baby kick, I felt the baby kick for 3 days pretty consistently through out the day and especially at night. Three days ago, everything just stopped. I can't feel any momvement at all. Any others like this? Should I be worried?