When to go to er for dehydration

When should you go to the er for dehydration? My heart seems to be pounding pretty hard, I threw up last night and have been nauseas all day, I'm exhausted, lightheaded when I stand up or bend over, I'm weak, and my head has been hurting on and off all day. I'm pretty sure I have an issue with my heart because I can feel it almost skip abreast sometimes which I feel is a little amplified. I know I'm dehydrated but don't know if I should go to the er.