My work over the years as pretty well been with the addicted populations, and they can be hostile enough as we might all acknowledge. I am also aware that any client has potentials to be hostile regardless. From my experience to be honest, I would very carefully examine the depth of our therapy if NO or little hostility was projected onto the therapist during a session. I mean in gestalt could it ever actually be advoided and continue to have the essence of gestalt? I believe not.
So you certainly have my vote that you have successfully gained your clients awareness and attentions in session. Great I say! Without tension very little is likely to be worked through.
As for the otherside of your message; that is, your admittance that you are having difficulties handling these situations again I say Bravo!
If we as gestalt therapists are not responding with our own discomfort and uneasiness then we are not authentically in session and we begin our own projections. Then we have mirror games going on and the whole thing falls out of gestalt and into something else entirely.
When I am challenged by my clients Claus, I experience similar difficulties as you briefly shared. For me I am simply at those times in agreement with the client that the session is not moving to a mutually closed gestalt. So, I as truthfully as I can muster, search the clients and my own awareness for the seed of truth within the projections and retro-flections of both the client and myself. If I am out of line within the session I admit freely to my disservice to the session, and this usually brings more authenticity to the session. Thereafter, the client is willing to explore the much more likely position that the client needs to work through the session in empathy to my gestalt abilities, and not in sympathy to my session failings. The client is of course not in session to give professional feedback. By rights then s/he naturally would be hostile to my slightest failings. So be it.
It's part of what gestalt is all about. Persons engaged by mutual agreement to be in empathy with each other but for different reasons and goals. Closing these kinds of open gestalts MUST be challenging BOTH to client and therapist, or from where is the gestalt salted? Gestalt without taste will soon be spit out.
So whatever, Claus. Admit your difficulties to your client, and close the newly open gestalts like you would any other. It sounds like you are taking the difficulties personally. Thank God Claus, I say. The last thing a gestalt session needs is the therapist not to be present, personal and honest.
And as a somewhat darker suggestion Claus, sometimes us therapists need a session or two working with other therapists in a simple but elegant "scream at me awhile why don'tcha? .... it feels soooo good when you stop!!" Peer work groups almost always improve ones "situations".