If so, you may well be suffering from stress. This is a perfectly normal reaction to the excessive and unrealistic demands that have been made upon teachers in recent years. Stress is a confusing term because it can describe both the things that make you anxious and your physical and mental reactions to them.
Anxiety is a more helpful word.
It is when the body and mind are fully alert. This pattern of behaviour can be traced back to our earliest ancestors. When faced with a carnivorous monster the cave man had to choose whether to stand and fight or run away. Either way, his fear would generate a great surge of adrenalin which gave him the energy he would need to deal with this situation. His muscles tensed, his heart rate went up and his breathing became faster.