Sorry you had a fall. Such things can be highly traumatic.

Your friend I am sure is disappointed, but if they are philosophical about it then accept that and don't beat yourself.

I am not always good at remembering engagements so calendars, phone alarms and notes are there for me.

I find a big pasta dinner makes me even more forgetful because all the carbs pump up my blood sugar levels. I stick to a moderate protein low carb diet.

Sending the ecard was a thoughtful thing to do. If you can afford it maybe an extra special birthday celebration would ease both your pain and hers.