blood donor fatigue days later? (blood pressure, donate, pressure, time)

[Orion2]

I've donated several times and learned to eat well before and after. I do not recall being fatigued longer than the evening of donation but this time it's been a few days and my cognition seems to be slightly impaired as well . I'm wondering if anyone else has experienced this? I have rather low blood pressure and think that may be a factor but would like others' input thanks.