It is a panic attack - probably delayed panic. When you are having treatment, there is a lot to think about, a lot to get done, get through, get over. You don't have time to
think about big things, there are so many, mainly bloody annoying, small things to deal with and swat. So NOW you can panic. Just when you and everyone else thinks you should be "normal". Deep breaths. Concentrate on the fact you HAD cancer. If we spend our days worrying about every physical ailment that can affect us, every accident that can befall, we would be unable to do anything. Focus as much as you can on what you have achieved. And go on that holiday. Reconnecting with this extraordinary world will be a good thing. Happiness will come in its own time, possibly when you least expect it. A bit of wonder and a little bit of looking forward, not back, will suffice right now. All of this can pass - the hair (I looked like a geriatric poodle for months!!), the weariness, and at least some of the fear. When you get back from holiday, some one to one counselling about dealing with that brush with mortality may help. But right now, a holiday is possibly the best medicine. Take care, best wishes.