After having read here and according to the Holy Quran:
until the white thread (light) of dawn appears to you distinct from the black thread (darkness of night) [al-Baqarah 2:187]
I was under the impression that the actual time to take sehri is longer than the Fajr time set in calendar. The Fajr time for my city is
3:28 while sunrise is
05:36. I woke up late (3:40) for my sehri and since I had to also take my medication, I started eating and drinking till 3:58 but just now reading more about it, I realized that this "white thread" described in the Holy Quran is actually twilight not the actual sunrise. I checked it's timing for my city here and it is 3:28. So my question is, was my fast valid? and What should I do if it was not?