They aren’t lost days any more than sick days when you have flu, are lost days. You may need a day to recover/sleep/nurture yourself when having tricky times with therapy. That is NOT laziness/wasteful/indulgent etc. it’s necessary to keep your strength up, and to stay mentally and emotionally resilient enough to continue with the therapy.
I had therapy when I was in my early 20s. It was to deal with something huge. I had it on tuesday afternoons. I needed up going part time at work because I’d get so agitated on Tuesday mornings knowing I had to have therapy that day, that I couldn’t manage at work. Luckily I was living at home so could afford to.
It’s so hard. You are being courageous and sensible giving yourself the nurturing you need to get through this.