Three questions for "Survivor:"
1. If I understand you correctly, you have problems throwing someone with koshinage and a couple of other techniques, but you don't have problems being thrown in those techniques. I would think it would be both, and that being thrown would be the more stressful of the two. If my understanding is correct, why do you think ukemi is less difficult (since you're just as close to your partner)?
2. Posters have offered you good advice (I think), namely to see a therapist, confide in your teacher, or to gradually desensitize yourself to stressful situations, and you seem to have rejected that advice, which is certainly your privilege. What sort of advice are you looking for? For example, would you like someone to post, "I was in exactly your situation, and my problem was solved by ...doing X as I was performing the technique, or ...doing Y just before uke attacked, or ...doing Z before class began?" If they know what you're looking for, posters may come up with more acceptable suggestions.
3. At what point in your aikido practice will you have to perform koshinage (e.g., in testing for nikyu)? Can you simply avoid that technique until then? Lots of students sit at the edge of the mat while the class performs suwariwaza ("I have bad knees") or techniques requiring a forward roll ("I'm recovering from my separated shoulder") or nikyo ("carpal tunnel syndrome"). If you can simply avoid koshinage now (with whatever excuse you like), perhaps you will be better prepared for it later.
As far as the first ones, goes, I completely froze up on koshinage, that includes taking ukemi for it. As far as the others go, you are correct, I can take ukemi for those techniques with no issues. I would hazard a guess that because I am concentrating on helping the nage (I am one of the highest ranks at our school, so much of my practice is with people who have less experience than I do) that I don't have to think about my position.
I don't feel that I have outright rejected any advice, other than discussing with my Sensei. As far as counseling is concerned, I'll agree that it could be quite helpful, but at this time, I do not have either the time or money to be able to go to counseling, since I don't know of any therapists who work outside of a pretty standard 9-5 type work week, and I don't have the available funds to pay even a small amount, so that is kind of a non-issue for right now. I will agree that desensitization would be a great thing to work towards, but I'm not sure how to go about it.
And I will be testing for ikkyu within the month, and there is a koshinage on the test. I have been using an injury as an excuse to sit out of some techniques, but that is turning into a crutch that I don't feel is healthy.