I wish my therapist happy holidays and bring him a gift on our last sessions before winter breaks. I usually don't send other texts / emails because I feel as if we already celebrated Christmas together.

Personally, given that my therapist is generally okay with outside of session contact, I wouldn't worry about sending a holiday wishes message if I felt like it - I'm sure not all his clients do that and they're not unmanageably many anyway, and personally I think good wishes are always welcome at special times like these. But it depends on your specific therapeutic relationship (as well as the therapist - I'm sure a therapist who never allows out of session contact or who has too many clients would not be so pleased).

I was actually thinking of wishing my therapist a happy new year via text this year but I'm not sure about it yet - not sure if I want to send any wishes this year. I'll live and see ...