It differs each time. I had two instances in which I was having d* all day, then got n* but never v*. I have also had an sv* where I v* 3x then had a d* off and on throughout the next couple days. Also, I once had some strange illness in which I had one bout of d*, felt better, then got n* like 5 hours later, had dry heaves for about an hour, then v* once. I was completely fine the next day though so I dunno if that case was an sv* or something else. It was a super hot day and I hadn't been drinking much water, so it could've been heat stroke. But yeah, I'd say not always, but in most cases, the v* comes first.