Has your cancer treatment put you into menopause? If so, it could be that. As the Letrozole dries up the last remaining drops of oestrogen in your body, menopause symptoms ramp up again. Menopause can make you anxious, irritable, quick to anger, depressed and give you mood swings... And that's all without a cancer diagnosis! So maybe your body chemistry is in turmoil while it adjusts and for you that's manifesting in your emotions.
I haven't had this specific reaction but I have gone from being a rather dry eyed individual to being the opposite. Currently it's ridiculously easy to upset me; I feel absurdly tender.
Definitely talk to your doctors about it. I'll bet they recommend counselling. Which certainly won't hurts. 50% of people diagnosed with BC will develop depression. Get on it quick if you think that's what's going on. My life is considerably better since I started taking the sad pills. I don't want to be on them forever but I need to process what's happened to me and feel fully recovered before I try to come off them. I deeply resent my compromised quality of life and I need time to come to terms with it.
Make any sense?! K xox