As excuses go...

[Nailshut]

Some has just dropped out of an event on Sunday because they're not feeling 100% after giving blood yesterday 🤣

Tbf I was once given the go ahead to give blood, despite the finger prick test just prior not reacting as it should.
It left me so anaemic I could barely stand, and felt awful for around 4 months until I boosted my iron levels back up, so I wouldn’t judge someone else not feeling well after donating.

Sounds very reasonable to me

We used to use feeling tired after blood giving as an excuse to go to the pub in the 90s absolute lightweights

I get you might feel a bit tired next day, but how does she know now she'll feel like that on Sunday?