Juliet's monologue before drinking the potion (4-3-008 through 4-3-044 in the source) is structured as a systematic confrontation with fear. She doesn't suppress her fears — she names them in order: the potion might fail; the Friar might have poisoned her; she might wake too early; she might go mad in the vault; she might see Tybalt's ghost. She works through each one. The terror escalates until she seems almost to hallucinate — and then she drinks. This is not courage as the absence of fear. It is courage as the decision that comes after fear has been fully acknowledged. That structure makes it one of the most honest depictions of bravery in Shakespeare.

In 4-3-010 through 4-3-015 (in the source), Juliet actually considers whether the Friar might have poisoned her. She reasons her way to trusting him — he's been a holy man his whole life, his reputation is consistent. But the question itself is not paranoid. It is correct. The Friar does have a motive: he married them secretly, and if Juliet were forced into a second marriage, his reputation and perhaps his life would be at risk. Juliet is not wrong to consider this. She just decides, reasonably, that his track record tips toward trustworthiness. That decision is correct — but it won't save her.

Among the horrors Juliet lists in her vault fantasy is the sound of mandrakes being torn from the earth (4-3-033 in the source). The mandrake root was believed to shriek when pulled from the ground — a shriek that could drive anyone who heard it mad. Juliet is imagining waking in a vault surrounded by her dead ancestors, with Tybalt's barely-buried corpse nearby, in the dark, hearing sounds that could unhinge her mind. The specificity of the mandrake detail tells us she has thought about this carefully. This is not vague dread. She knows exactly what she fears.