Feeling faint on standing after starting methylphenidate or Concerta XL

[Blueswan3]

Anyone any experience with methliphenadate/concertaxl
I've been feeling faint when I stand up about 4 times
Once after swimming and walking ,once after getting out of the car and once in a hot stuffy environment,but all times it happened when I stood up
Blood pressure was 122/70 when I went on medication,and 4 weeks later it's 118/67.
Never had this in my life before BMI is 30
Have notified ADHD provider,but no response yet

Are you eating enough?

Ah thankyou ,an actual reply .much appreciated
No actually that was the conclusion I came to after I realised I'd not eaten or drunk anything each time it happened.
So snack first thing before I get up or leave the house