Suggest Remedy For A Neuromuscular Disorder

My 19 yo daughter has a neuromuscular disorder (congenital myasthenia) and has had several episodes of tachycardia (150-220 bpm). Prior episodes were discovered to be related to excess caffeine combined with OTC decongestants. She has been symptom free for about a year. During that year she stopped all caffeine intake, and no longer takes decongestants with colds. However, she recently had another episode for several hours that was initiated by hiccups. She started the hiccups, got dizzy, and her heart rate jumped up to ~170 bpm. Any causal relationship? She laid down for a few hours and drank water to boost her blood volume, but it took awhile for her to recover. Unfortunately, she was away on vacation when it happened. Anything that we can do at home to decrease the heart rate before seeing her doctor, if it happens again?