This is a subject about which I can speak with at least some degree of authority. If I give unrelated material, forgive me, but I think there may be extracts that you can relate to as well.
I've been where it sounds like you are now, and beyond. It was about two years ago now (I think) that I stepped from being where you are now to a complete and utter shut-down.
In my case, I was the stupid one. I didn't get help when I started recognising that things weren't right. I then allowed some severe trauma into my life (meeting family that I hadn't seen since being a wee child) and still believed that I would just cope. I then did something that, to this day, I can't speak about as it was so shameful, and that was the final straw.
I came home in floods of tears and within minutes it was like my entire life had gone into a fast reverse. Everything I looked at seemed too tall. Noises were too loud, lights too bright, and everything just seemed more scary than it should. At this point I can see exactly what happened -- my brain went back to being five years old and I was seeing and hearing everything as a child again. At the time, however, it was just beyond frightening.
I was submitted into the psychiatric part of the hospital that night. It's taken me a long time to be able to admit to that. These days however, I see it as little more than a means to an end. Sadly, as much as we try to paint it to the contrary, society still doesn't understand issues of mental illness.
After that and until I got my dog really, I managed to become a recluse. I lost contact with all friends and family and couldn't step outside. My feeling was that people could see what I could feel. Logically, they couldn't of course, but that is how it felt. I felt as though all eyes were upon me. I couldn't even walk near an open curtain in my house.
I was incredibly lucky in that my Doctor was extremely understanding. To this day I can't thank him enough. It pains me that we are moving counties now and I will have to change Doctor. It's comforting to know that I've had him if things were to take a wrong turn again.
He tried me on several different drugs. Most of them made me feel very ill, particularly with stomach pains and dizziness. We finally settled on EFEXOR, Venlafaxine and that was the one that seemed to work. Though, as I recall, it took several weeks to kick in. During this time I came about as close to killing myself as I'd ever like to come. I recall the lines of a Robbie Williams song: "I don't wanna die, but I ain't keen on living either." which was pretty much how I felt. Each day seemed longer than the last and I would have been thankful not to have to see another one.
During that time, I had the help of a social worker (bizarre too as that is what my partner does), and a psychiatrist. I personally couldn't gel with the psychiatrist and so the Doctor, Social Worker and I all agreed not to waste his time, as they are extremely busy people. The Social Worker tried to get me to join clubs and such like but alas that was too much for me at the time. I just felt trapped and needed to exit as quickly as possible.
But, knowing that I could speak to the Social Worker was a comfort in itself. We men aren't very good at revealing our feelings generally and so I didn't feel that I could explain my feelings elsewhere. Even to my partner who showed and still shows nothing but complete support.
A year or so ago I realised that I couldn't stay locked in the house all of the time. Not only was I wasting my life, but my partner's too. It dawned on me that I would feel safer with a dog at my side. No idea why now, other than perhaps she would get the attention of the eyes that I felt would otherwise be on me. She would also need walking and, as unfeeling as some may think I am, I can't not walk the dog.
Since then I haven't looked back. I'm out for three hours a day, I meet people on the walk and have acquired a couple of people who I consider to be friends doing that, I walk into town, etc. Could I visit a pub? Probably not. I still don't do crowds of people, but I will. I've stopped smoking this year, completely changed my diet, and am even looking at changing what I do for a living.
Coming off the pills was an episode in itself. We had to do it really slowly as there was acute dizziness without them. We just lowered the dose by 50mg each couple of months. The most important thing about the medication was that my GP always made me feel that I had 100% control of it. There was no hurry to go on them or come off them.
My point is that no matter how bad things seem, and believe me, I know that they can often seem intolerable, things can and do change.
There is no sense to why you feel like you do. You'll drive yourself nuts trying to find the sense in it. Try to learn to accept that you are as you are, for now. Forget those who give the infernally annoying and ill-informed "sort yourself out" type of responses. They can't see a cast or a bruise and so they can't grasp that something can be wrong.
There are no quick fixes and there doesn't need to be. You have a whole lifetime. For me, the dog, the brilliant support offered by the social worker and my GP, and above all, time were the best healers. For you, it may well be something completely different. But it will come to you in time, I'm sure of it.
As for practical solutions, a toughie as we're all so different. I have found that holding a bunch of keys in my hand as I walk about really helps me. I can focus on the keys and not on what is going on around me. Sounds silly I know, but...
I hope that you can find someone in a professional capacity to talk to as it really helped me to get to the root causes. There are some things that I've had to learn to accept about myself and accept that I may never be able to sit in crowded pubs, for example. But, the list of things that I can now do grows almost weekly.
Truly, I hope it works out for you, and if you need an understanding word, just drop me a PM or something.