At two in the morning, a mouse behind the skirting board sounds like a person in the kitchen. The noise is tiny. The interpretation is enormous.
Fear works through amplification. A single thought about Monday — perhaps four seconds of actual content — gets replayed at a volume the body responds to as though the thing were happening now.
Which means the raw material is often small enough to write on a card. Try it sometime. The dread fills a room; the sentence underneath it fills a line. Same information. Very different size.