Is it normal for anxiety attacks to come out of the blue?

Lately I've been having anxiety attacks and they aren't triggered by anything, they just happen. Or sometimes a voice will just pop into my head and tell me I suck or how bad I am at writing things (I write stories on wattpad) and then my whole mood drops and I can never explain it. Is this normal?
Is it normal for anxiety attacks to come out of the blue?
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