I have been thinking of a different way of giving how I react to this sort of thing. I worry that the therapist will use the extra time against me - it will cost me too much (not money as such) - the potential price of the staying over will be more than the potential benefit. I am not worried about me being a boundary basher - I assume others can hold their boundaries just like I can hold mine - someone bouncing against my boundaries does not especially upset me in that gut fashion that it does for some. I fear the expectation from the therapist that the extra time will accomplish something (that I will fail at), or will be used against me in some manner by the therapist (I am not saying this is a rational fear).
Mine is still the same inability to accept something like this as a gift - but from a different fear than some of the descriptions here perhaps. And perhaps a different control. I think both (or more) are an attempt at control - just perhaps different types.