There are many different forms of anxiety, but it may be helpful to think in terms of three fundamental kinds: instinctive anxiety, traumatic anxiety and cognitive anxiety.
‘Instinctive anxiety’ is based on threats or dangers to our survival. This is what we experience while walking near the edge of a high cliff, in deserted city streets at night, or when someone verbally abuses us or threatens us with violence. We instinctively feel anxiety in such situations, as a warning to be on our toes, or to flee from the potential danger. Instinctive anxiety is healthy. It has evolved over tens of thousands of years of human history, and we probably wouldn’t be here without it.
‘Traumatic anxiety’ is related to traumatic life experiences (usually in early life) that have left behind some degree of psychological sensitivity and vulnerability. Traumatic anxiety arises very strongly when we face situations that remind of us of the original trauma — for example, when a person who experienced abandonment during their childhood starts a relationship as an adult, and finds that their fear of abandonment arises again, filling them with insecurity. Another example is an ex-soldier hears explosions or screams, which rekindles the trauma he experienced in conflict.
Finally, there is ‘cognitive anxiety.’ Sometimes this acts upon instinctive anxiety, picking up on dangers and inflating them. For example, fear of flying begins with an instinctive sense of danger, which for most people quickly fades away as they get used to flying. But for others, this instinctive fear is inflated by thoughts — for example, imagining that the plane might crash or that someone might open the emergency exit, picturing themselves five miles above the ground, remembering stories they’ve read about plane crashes… In a similar way, a person who is walking through the countryside as night starts to fall might imagine that wild animals are creeping towards them, or that people are waiting behind trees to attack them.