Wash your face with cold water to wake yourself up.
Tips
usage
洗脸 is a verb-object phrase - you can split it: 洗一下脸 ('wash your face a bit'), 洗了个脸 ('gave my face a wash'). Related daily-hygiene verbs follow the same pattern: 刷牙 (brush teeth), 洗头 (wash hair), 洗澡 (shower).
