A boundary to your inner, personal life (represented by the intimate activity of taking a shower).Having to take a shower without a curtain can mean:
(If not by choice) You're feeling exposed, or forced into a vulnerable situation in real life somehow
(If by choice) You're feeling secure, open, honest, and not feeling like you need to hide any secrets from others in your life
Someone intruding on you while you're taking a shower can represent someone crossing your boundaries, taking advantage of you, or "intruding" on your life somehow in real life.