Hiccup, or singultus, is an involuntary spastic contraction of the inspiratory muscles. Though usually a benign and self-limited annoyance, hiccups may be persistent and a sign of serious underlying illness.
The exact pathogenesis of hiccups remains unknown. In most cases in which a specific cause can be assigned, hiccups appear to result from stimulation, inflammation, or injury to one of the nerves of the hiccup reflex arc.
SARS-CoV-2 has been known to show selective neurotropism to areas of the brain controlling respiration,  which also control the hiccup reflex arc. Irritation or stimulation of this neural area can be a plausible explanation for hiccups in Covid-19.
Several case reports have been published ,,,,,, which report hiccups as a symptom of Covid-19 and a study  that proposes hiccups as a specific neurological symptom in males.
Hyponatremia is defined as serum sodium concentration less than 135 mEq/L and is the most common electrolyte abnormality encountered in clinical practice.
Joint European guidelines classify hyponatremia in adults according to serum sodium concentration, as follows: Mild: 130-134 mEq/L Moderate: 125-129 mEq/L Profound: < 125 mEq/L
Acute symptomatic hyponatremia is a medical emergency; a sudden drop in serum [Na+] can overwhelm the capacity of the brain to regulate cell volume, leading to cerebral edema, seizures, and death.
Hyponatremia both asymptomatic and acute symptomatic has been reported to be associated with Covid-19 in many case reports. , , 
Hyponatremia in Covid-19 can be caused by either SIADH or inflammatory cytokines, IL-6, or a combination of both. 
This is the first case that reports upon both acute symptomatic hyponatremia and hiccups to be present simultaneously, in a Covid-19 patient.
Both hiccups and hyponatremia can develop in a Covid-19 patient independently, however, hiccups can be triggered by many metabolic disorders, hyponatremia being one. 
It’s difficult to say if, the hyponatremia developed first which precipitated hiccups or both hiccups and hyponatremia developed independently.
However, resolution of hiccups with improvement in serum sodium levels points more towards metabolic etiology.