Birthdays always trigger emotions for me and I think you have to take that into consideration.
Generally people will not know how you are feeling and we get very good at hiding how we really feel.
I love my partner dearly but he does cause me unnecessary stress. He also doesn't know how I feel, what things set me off or know when I need calm and we've been together for 25 years.
Wired, you have to find a way to protect yourself from those hypes of stress and anxiety. Have a 'time out' switch. Go to those things that give you calm like your programmes, your flat improvements, a walk, time with your dog, whatever you need at the time.
Mental conditions are hard because no-one sees them and we fight hard to lead a normal life and most accomplish that.
Take these sort of days and learn from them and when another one comes along you'll know it's just a difficult day and to not put too much emphasis on it.