Hi and welcome to the Chiari forum.
This can be reflux...acid moving up into ur throat...it can happen if u bend over or with a hiccup....sometimes it is so bad ne movement can cause it to rise up.....
U may have PND(post nasal drip)...which can cause the mucus u mentioned and it drains into ur stomach and can cause nausea and reflux.
Stress can make u feel worse so do try to relax and modify ur diet and lifestyle,...,see the Health pages for tips of foods that r safe and foods to avoid and lifestyle tips that can help as well.-http://www.medhelp.org/health_pages/list?cid=236
I feel I'm in a similar situation as you (in terms of symptoms and fear of vomiting). In fact I'm 31 and haven't vomited in 20 years, due to my extreme fear. Hopefully I can give you some advice/help from a similar experience of yourself (meaning I wont tell you to do anything that will in any way make you fearful of vomiting).
I take 150mg of Rantidine two times a day; once in the morning and once at night. This medicine is available over the counter, or by prescription. It is used to treat GERD, which it sounds like you have. I also believe I have it. I constantly have a mass in the back of my throat, which is worse after eating. I can even feel water coming up the back of my throat after eating. I also have the mucus you describe, which can also be a symptom of acid reflux. Hopefully the randitidine for two weeks will help ease your symptoms. Often I find that is not enough and I find myself eating tums (2-4) and hour when my symptoms are really bad. I also find that I have "air" trapped in my upper throat, which scares me so much. I can feel is coming up and it literally stops me in my tracks. I have to stop, and force the air out. This always brings anxiety as I fear I will vomit (although as I mentioned above, I have yet to, in 20 years).
I think it would serve you well to learn about GERD (or acid reflux) and recognize that all the symptoms you describe can be attributed to that. Once you realize what is happening, and what you can do to treat the symptoms it may help ease your anxiety regarding the situation.
I know very well the anxiety you describe when this happens. I've found one of the best things to do is relax (easier said than done! When I feel the acid/mass coming up my throat I usually go lie in by bed, in a sitting position, and listen to a guided meditation called "Healthy Body". It really helps me to relax and to realize all the processes that are going on are normal and natural, even though it feels otherwise. By the time it's over I'm usually calmed down and have lost that panic attack feeling brought on by feeling as if I will vomit.
I also experience extreme gurling on the left side of my stomach, which I've realized happens when I am hungry. It feels as if there is a gallon of water sloshing around inside me. If I breathe out hard, and from the stomach, I can actually cause the gurgling. This also causes a lot of vomit related anxiety, and I over come that by eating a small meal (say a fruit, or a cucumber) and it usually goes away. It can be VERY scary to have symptoms in the GI tract, especially for someone who is afraid of being ill.
I wish you luck, and just know you are not alone :)