Acute ulnar neuropathy at the wrist can be difficult to diagnose, as it is an uncommon neuropathy with variable clinical presentations and numerous etiologies. We present a case of acute ulnar neuropathy of the deep motor branch caused by a ganglion cyst in Guyon's canal. Interestingly, this case of acute loss of motor function occurred after the patient participated in yoga (specifically the downward dog position), and resolved spontaneously over time after stopping yoga, without surgical excision of the ganglion, suggesting exacerbation or protrusion of an occult ganglion cyst due to increased activity and compression of the hypothenar eminence.