Honestly, if you are that scared, I wouldnt trip. Mushrooms have a (relatively) high incident of bad trips, and most of those are going to occur from anxiety.
But if you insist on taking them-
Nausea has never been a big problem for me, but I've heard that ginger helps.
You shouldn't take them on a totally empty stomach, but eat a light meal maybe 3-4 hours before with fruits, vegtables, and simple proteins being the most present items. Stay away from fats, oils, complex carbs, meat, dairy, etc.
A good starting dosage is between 1/2 and 1 gram, especially considering your anxiety. A small dosage will not necessarily make you less nauseos, but it certainly won't make you more (if that makes sense...everybody if affected differently).
Mushrooms can be scary, because they tend to be confusing. If you cannot handle confusion well, yes, you may get scared. However, it is extremely unlikely that you will see rivers of blood or anything like that (although it can and has happened).
The "breathing" that most people mention is just a movement in flat objects. It's really not that scary. If you do start getting scared, the best thing you can do is to remind yourself that you are tripping and it is not real, and it will end. Having a trip-sitter is also a very very good idea.
If you have a bad trip, the best thing you can do is learn from it. Try to identify why you had a bad trip and what overarching problems in your life caused it. You are extremely unlikely to stay scared forever, unless you have a family history of extreme mental disorders.
Again, I would reccomend not taking mushrooms at this time. Acid is friendlier, but even that I would say might be too much. Mescaline would be the best, but true mescaline isnt found on the streets, and dont trust anyone that says they have it.
http://www.erowid.org/plants/mushrooms/mushrooms.shtml