If you can't keep anything down, not even sips of water, go to the hospital.
If the pain is so severe that you can't stand it, and I mean really can't stand it, then you'll know you have to go to the hospital because you'll know you're going to die otherwise, that's when you go to the hospital.
If I can keep liquids down without throwing them ALL up, and I can tolerate the pain, even if it's really bad but I can take it, then I stay home. It's more comfortable at home and I can put me on clear fat free liquids and take pain meds at home just like they'd do at the hospital.
Not only that, but if you don't go until you have no other choice, then they tend to believe you when you do go. I've had ER docs accuse me of just wanting meds and then ask me how often I go to the ER and when I tell them I've had CP for 13 yrs and I've been to the ER 5 times, they just shut up and take good care of me. They believe me.
Everybody has to decide for themselves when it's time to go. In my opinion, if you have to ask, then you probaby don't need to go.
Ronda