I went to the doctor and told him I felt like a curtain.

This joke is a fantastic example of wordplay, specifically a pun that relies on the double meaning of a common idiom. The humor springs from the unexpected literal interpretation of a phrase that we usually understand metaphorically. When the patient says they feel like a curtain, it primes us for a physical description, but the doctor's punchline cleverly twists this into a piece of advice that also literally applies to a curtain.

The phrase "pull yourself together" is an everyday expression, commonly used to tell someone to regain their composure, calm down, or get their act in order. It's advice a doctor might genuinely give to a distressed patient. However, a curtain can literally be "pulled together" to close it or tidy it up. The joke plays on this contrast, taking a serious piece of medical advice and making it absurdly literal in the context of a drapery-like patient, creating a lighthearted moment of comedic misunderstanding. It’s a classic setup for a quick, witty laugh.