Benign intermittent limb paresthesia: Given the transient nature of the symptoms ("feeling asleep") and the absence of objective weakness on examination, this condition is a plausible explanation. The normal lab results and lack of progression over time also support this diagnosis.

Electrolyte imbalance: The elevated potassium level (hyperkalemia) could contribute to muscle weakness, although it's not typically associated with unilateral symptoms. The slightly elevated creatinine suggests possible renal involvement, which could lead to electrolyte imbalances.
Vitamin or mineral deficiency: Although B12 levels are normal, other vitamin or mineral deficiencies (e.g., magnesium, calcium) could cause muscle weakness and paresthesia. However, these would typically be associated with more systemic symptoms.
Musculoskeletal or nerve entrapment: Conditions like thoracic outlet syndrome or a cervical radiculopathy could cause unilateral arm weakness and paresthesia. However, the absence of objective findings on examination makes this less likely.

Stroke or transient ischemic attack (TIA): Although the patient is young and the symptoms are intermittent, it's crucial to consider vascular causes, especially given the unilateral nature of the symptoms. A thorough vascular evaluation, including imaging (e.g., MRI), may be warranted.
Multiple sclerosis: This demyelinating disease can present with unilateral weakness and paresthesia. Although less likely given the patient's age and lack of other symptoms, it's essential to consider, especially if the symptoms progress or worsen.
Spinal cord compression: Conditions like a herniated disk or spinal stenosis can cause unilateral weakness and paresthesia. Given the potential for serious consequences if left untreated, this diagnosis should not be missed.

Peripheral neuropathy: Conditions like Charcot-Marie-Tooth disease or other hereditary neuropathies could cause unilateral weakness and paresthesia. However, these are relatively rare and would typically be associated with a family history or other systemic symptoms.
Mitochondrial myopathies: These rare genetic disorders can cause muscle weakness and other systemic symptoms. However, they are unlikely given the patient's age and lack of other symptoms.
Neoplastic or paraneoplastic syndromes: Although extremely rare, it's essential to consider the possibility of a underlying neoplasm, especially if the symptoms progress or worsen over time.