This is not one which many folks will ever experience but I'm posting it to reinforce the idea that a good diagnostic work-up is important.

Like that old saw: "when a hammer is the only tool you have, everything turns into a nail", just because we "know" what a Cluster is does not guarantee that we "know" every Cluster situation.
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Cephalalgia. 2010 Dec;30(12):1509-13.

Positional cluster-like headache. A case report of a neurovascular compression between the third cervical root and the vertebral artery.
Créac'h C, Duthel R, Barral F, Nuti C, Navez M, Demarquay G, Laurent B, Peyron R.
SourceUniversité Lyon 1, France. christelle.creach@univ-st-etienne.fr

Abstract
Symptomatic cluster-like headaches have been described with lesions of the trigeminal and parasympathetic systems. Here, we report the case of a 44-year-old woman with continuous auricular pain and a positional cluster-like headache associated with red ear syndrome. Clinical data and morphological investigations raised the hypothesis of a neurovascular compression between the C3 root and vertebral artery. Neurosurgical exploration found a fibrosis surrounding both the C3 root and the vertebral artery. The excellent outcome after microvascular cervical decompression SUGGESTS A CAUSAL RELATIONSHIP BETWEEN THE CLUSTER-LIKE HEADACHE AND THE VERTEBRAL CONSTRAINT ON THE C3 ROOT.

PMID:20974591[PubMed]