I agree with those above about holding the therapist in mind, but would just like to add a bit more to it. Small children aren't able to hold inside the image and love of their mom, so must have them in sight or very near until they grow to the stage where they can have enough of mom to feel her constantly there even while apart, at school, etc. Some us in therapy ( like me) are re-experiencing our early childhood with T at the stage where we can't hold T in mind and the separations between sessions, especially vacations, etc are excruciating anxiety and grief. My T explains how I need to have enough of her presence and gentleness for a long enough time that my inner child builds up a "bank account" of good relations to hold me together better in absence of T.

So, it's good to be able to talk about this stuff to the therapist so she can tell where you are at inside so she can try to make the schedule even for you, or go twice a week, etc. Tho therapists are assumed to be mind readers, sometimes they can fail to realize some things that really hurt you until you can tell them directly. My parents would use my fear to tease me, and I was paranoid about letting T know. So I finally got enough trust to tell her how horrible it was for me to skip sessions, etc. She was careful then to keep my sessions even.
We don't learn to be apart by just practicing at it, but by building a foundation of good relations with T that make independence come naturally. We missed all that stage in childhood, which is why we re-do it in therapy.
I came from an abusive background where admitting fears and needs would make my parents do more to me on purpose to make it worse, or to try to make me strong by forced separation (which didn't work at that age).
Then, just this past year at T's vacation time, I realized to my amazement that I didn't feel so deep anxiety at her being away, as it seemed like she was sort of with me anyway. It was hard to wait but not nearly so bad as the years before. But that came by building a relationship with T that made a thick, woven cushion inside of strengths and memories. Actually,ironically, this relation with T doesn't make us more dependent but instead gives us a foundation we missed, from which we can feel OK to explore out in the world, and actually builds into more true independence.
That's a very important part of therapy for us who have had rejection and deprivation in early life. And I think this is also what your T means by being held in mind.