Hiccups are a common nicotine OD symptom. For me, if I stop vaping when they come on, I stop, have a good drink of water and wait 20-30 minutes and I'm fine. If I power through, I'll start getting nauseated and a headache - not good. It's worse if I get juice in my mouth; almost instantly get the niccups. FWIW, I would occasionally get niccups when smoking analogs, especially if I chain-smoked 2 or 3 in rapid succession.