ahem.
If she was just knackered then she is guilty of being unprofessional and unethical.
However, two other things could have been going on:
It is very useful and can be extremely productive if a counsellor goes into kind of a reverie when with a client....going 'inside' as it were....did you find what she did say useful?
Secondly, there are particular kinds of presenting problems that can create a strong almost irresistable urge to fall asleep in the counsellor...it is a known phenomenon and has been written about in journal papers in the psychotherapy domain.
I think both of these are unlikely in a first session, which should be about putting you at ease and creating a sense of safety, which she patently did not do.
However, I would strongly urge you to go back and confront her....tell her how offended and put off you are by her having appeared to fall asleep...see what she says. the worst that can happen is that she fobs you off and leaves you feeling the same, in which case you should of course complain to the practise manager in the first instance. You might find though, that you are pleasantly surprised by her response to your honesty.
She might be a totally sh*t counsellor....but I only think you'll really know that by her response to you.