How long before vomiting and diarrhea become serious?

It is serious from the beginning, especially if you are vomiting blood. You only have so much fluid in your body, so after the initial "evacuation", (unless you are crazy enough to go eating a heavy meal again...) you run the risk of dehydration. Dehydration depletes your body of vital minerals and nutrients which organs like the heart and liver need to function properly. If you cannot retain anything in your stomach for at least 24 hrs. you need to at least suck on ice, or drink small amounts of an electrolyte drink like Pediasure for kids to replace the potassium and magnesium your heart muscles need to keep working. If after 48 hrs. you are still vomiting and the diarrhea has gotten worse, you definitely need to go to the hospital. You may need an IV to stay alive. You can live for at least 72-96 hours without any food, but you need fluids, definitely.

Two or three days before severe dehydration sets in. If combined with a fever, it is evidence of an infection. I had all that going on for three days and I ended up in the hospital with a kidney infection that had spread to my blood stream, so go to the doctor sooner rather than later.

I'd be tempted to call the doctor after 24 hours. The biggest threat is dehydration. Make sure you drink plenty of fluids.

WebMD recommends 24 hours - here's the link for more info

http://www.webmd.com/content/article/90/100639.htm

anything over 48 hrs id say... but going to the dr anytime is not a big deal.. just go now and get it over with

Not long...a body can seriously dehydrate quickly..get some medical help.

2-3 days

If the tongue is dry,this means severe dehydration.

its better to prevent that be sorry afterwrds so i recomend going to a doctor