I have a question from Pilgrim's Progress: 2. When the Giant is in the sunshine he is overcome by "fits." Why do you think this only happens in the sunlight?

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Casting of light on despair. Despair, despondency, represent darkness. Shaking, or "fits" (turmoil, angst) occurs in sunlight as light overcomes darkness.

maybe because he is used to being in the dark

The giant represents Despair, right? Well, despair is like a cloud of darkness that overwhelms us, and when the rays of the Son shine upon us the darkness and despair leave us.