I think being susceptible to your DH moods is very natural in this situation.
My DH was just about as positive as it was possible to be (mainly because his default reaction to things not going well was to stick his head in the sand and pretend to everything was okay and just carry on with his life).
I actually found that quite hard at times as last year he was determined that the various medical and alternative treatments he was undertaking would, if not cure him at least mean his cancer didn't really effect his life. Whereas having been told he had a life expectancy of around 12 months I just couldn't view it like that.
Nonetheless, his attitude meant that he could continue to enjoy life as much as possible, and that meant that I did to.
I had to let him do it his way, there was just no way that I could disabuse him of his mindset, it was what he needed to keep going.
But, when he was in the post chemo physical dip it really impacted on how I felt and my emotions.
As you say, realising that, and seeing a couple of cycles and him being better again after the dip, helped me deal with the later cycles.
I also k kw what you mean about the bank holidays etc. DH was diagnosed and undergoing initial treats during the junior doctors strike last year and everything seemed to take forever. His initial consultant appointment, following scans and investigations always the week of the May bank holiday, and you just want everything to happen NOW.
In reality clinic was Wed and tests were still being determined, so things couldn't have happened quicker. But we only really found that out as time went by and we got into the system.
Big hugs x