Where does tiredness fit in the model?

Hi there,

I’m wondering where tiredness would fit in the model – is it a circumstance or a thought? I guess I can see how it can be both, like if you think the thought “I’m tired” that could cause you to feel even more tired? But what about when it is a circumstance – so you are physically tired eg. from not sleeping. How do you know if it should be a circumstance or thought in your model?

Thanks for answering!