A 11 month old neurologically impaired baby is admitted to the pediatric ward. The child is under evaluation for cerebral palsy. The mother repos episodes of regurgitation, aspiration and frequent respiratory infection in child. A provisional diagnosis of GERD was made. After few days of being in hospital, mother complained that she noticed child's back arched suddenly, with splaying of head and legs outwards which became stiff. The intern posted there rushed to the bedside where he noticed spasmodic torsional dystonia with opisthotonic posture. This episode lasted 2 minutes. Thereafter multiple episodes where noted. Electrolyte and biochemistry panel revealed normal findings. Which of the following is the most probable diagnosis?