Glad to get your response!
Wow, "It's all in your head." I love that line. I've heard it from more than one person, myself. I think people who say such things are, fortunately for themselves, so free from this sort of anxiety that they're simply incapable of understanding it. Oh, to be free like that.
It's really remarkable to read the details of your struggle with this issue. It's just like reading a diary entry from my own head. The bit about needing a bathroom set back from the front door of a hotel room--I identify completely. In fact, having been an apartment dweller for several years, I have discovered that this is true for my residence, as well. I live alone, but if there is enough ambient noise permeating the walls of the bathroom, I do not feel sufficiently alone, and this can prevent a normal bowel movement. I have even sought new apartments which would better provide this sense of solitude. Most unfortunately, the place I am in now has proved to be uncomfortable. When I first checked out the space, it seemed to be very quite. After I moved in I discovered that any cabinet doors/bathroom fans being turned on in the apt to the left can be heard through the walls. Because my apt is essentially a one-room space with a bathroom, this really invades my privacy. The only time I can REALLY relax and completely relieve myself is when I know my neighbor is at work, so there is no chance of my hearing him through the wall as I am doing my business. It's completely irrational, because I know that any sound I may make while I'm "unloading" will not be perceptible to him in the other apartment. Thus, weekends are never as relaxing as they ought to be, because when I get up in the morning I do not have my normal sense of privacy as my neighbor is home, just on the other side of the wall, ready to spoil my solitude with the slam of a cabinet door. It will be another 6 months before my lease expires and I can look for a more suitable apt.
Having studied psychology as an undergraduate, my interpretation of this problem is a case of run-away maladaptive classical conditioning. Through a series of stressful experiences while in the loo, however minor, the sufferer's psyche has become so attuned to any disturbances that the subconscious criteria for feeling "alone" becomes more and more stringent. Of course we realize that there is no real threat coming from friends or relatives while we are in the bathroom; for that matter, there is no real threat coming from strangers outside a stall in a public bathroom. But this need for solitude in some of us is an unfortunate but very real consequence of our inherited psychology. I take comfort, at least, in knowing that other people share this same profile--people who seem to be otherwise well-adjusted. Makes me feel like less of a looney.
I also understand what you mean by having to trust a person. I may have mentioned in my last entry that the girl who stayed the night at my apt was not someone with whom I was completely comfortable with. When she left in the morning to give me some time alone while she shopped, I did not "trust" that she wasn't merely dawdling around in her car, impatient for me to finish. So of course these thoughts placed additional pressure on me, and I was not able to have a normal bowel movement. Another disappointment.
This response is long, but I want to respond to your major points. About traveling---I used to think that perhaps my bowel was simply averse to traveling, and that being backed up a little was going to happen on any trip. But I think I have discovered that if I drink enough water and eat the right foods, if I am guaranteed some privacy in the mornings (that includes a hotel room with a bathroom that feels secluded enough--not right next to the front door), I am fine. If you are spending long hours on a plane or something, that could account for constipation. And yes, know exactly what it's like to have your enjoyment of a trip completely interrupted by feelings of bloatedness. I am so much more pleasant to be around when I am regular. If I can only have that relief in the mornings, I am be the cheeriest member on any trip.
Last point: I really sympathize with that poor woman who has to rise early before her kids get up. Such a shame, not to be comfortable in your own house with your own family. I know this is what I have in store for myself, though. I am hoping that--with financial means--I will be able to purchase a house that has perhaps a little guest house in the backyard. Some place I can use for a study, that just happens to include a really private bathroom that is all mine. To live with a family and still preserve a complete sense of privacy at some location in the house would be a dream come true.
Do you find that you must feel as if no one is waiting on you, or even knows what you're doing? Knowing that nobody can hear me is not enough. I am affected even by the possibility that someone KNOWS I am in the bathroom, and suspects I am doing my business. To really relax, I must feel as if I could spend 2 hours in a bathroom, and nobody is going to inquire or talk to me or come looking for me. Hence the hope for a guest house.
Anyway hope this has been somewhat illuminating. If I post again, I will list some of the ways I have shown a little improvement through my thinking. I do believe that changing your thought processes is the key to making small improvements.