I'm not sure if I am understanding your note entirely-do you mean he "works himself up" as in crying so hard he vomits? Or does he just vomit? I'll answer as if he's crying, and I apologize if I'm way off track.
If he's crying hysterically at bed time, and you or your husband are there at 16 months, it probably means he's not secure falling asleep on his own and has developed a really strong way to resist. The vomiting is nothing more than a physical symptom of the severe crying. The only problem with soothing kids to sleep, is that they become trained to need it.
We always did a fun bedtime routine and then walked away. Yes, we wanted to cuddle all night, but we wanted the kids to feel good by themselves at bedtime, so they cried it out a little in the very beginning and that was that. We also avoided "feeding them to sleep" based on warnings that they would need to eat in order to sleep. Actually, my son (15 months) often takes a bottle to bed (I hand it to him and walk away), but not always, and he rarely cries, so I didn't see it as an issue, he tends to wake up hungry during the night if he hasn't had a late night bottle and if we've been busy and had a light eating day.
However, if your son is used to having someone with him, and he's used to nursing himself to sleep, you have to now make a choice.
A) Stay with him and sooth him and nurse him to sleep and wait until he outgrows this.
Or
B) make a change and deal with the strenuous adjustment. It will change if you persist.
The most important ingredient to kids sleeping all night is being full. But not just right before bed, they need to be fed to total capacity-even when they don't seem hungry-all day long. It takes several days for the body to understand it's fully fed, and then kids who have been waking up during the night suddenly sleep straight through.
You should increase his feedings all day, and try to wean away from the night time one. Or at least, nurse him before bed, but not to sleep, and then burp him thoroughly, and wait a half hour or so before putting him down. Then Walk Away. YES, he will scream and be inconsolable, but this is because he is breaking a lifelong habit you helped him build. Once he gets through it, days, weeks (probably not more than a week) he will be able to go to sleep on his own. You'll even be able to go back to nursing him to sleep if you want sometimes, once he gets it that he can sleep securely on his own, and screaming and getting worked up doesn't produce a parent to sooth him to sleep.
Don't think of the "mean" aspect of letting him cry. Think of the greater good of him sleeping peacefully when he feels secure on his own. Good luck whatever you choose-and GOOD WORK nursing so long!