Yes, that is a good point Artley. Having a medical condition or being under the weather is not something we can control.

However, I still think the onus ought to be on the T. In other words, being self-aware enough to know how this might impact a client. This is what they are trained for.

Typically, yawning, nodding off or other such non-verbal communication cues are interpreted as disinterest. Here the OP sensed a lack of engagement from their T. Ts' actions and words do have an impact on clients and this is something Ts need to gauge and/or modulate.

A simple acknowledgment (if they don't want to be too personal or disclose too much) would suffice - I've had a rough day... It's not you etc etc. But dozing and yawning on a client without acknowledging it can be damaging. Some clients might not want to comment on that, for various reasons. And again, the T is the one trained to attune to the client - not the other way around.