Can someone who begins a voluntary fast break it?
It is preferable for someone who begins an act of worship not to break it.
Allah the Exalted has said {what means}: "and let not your [good] deeds come to nought!" [Muhammad/33].
However, if a person starts a voluntary fast (nafl) and needs to break it, they are going against what is preferable, but there is no sin upon them.
Does excessive sleep during Ramadan invalidate fasting?
Sleeping a lot in Ramadan does not invalidate the fast, but a Muslim may miss out on great rewards from prayer, Quran recitation, and acts of worship due to excessive sleep.
What should someone do if they fasted for only 28 days in their country and then traveled to a place where Eid has already been declared?
If a person fasts in their country and then travels to another country where Eid has been declared, they must celebrate Eid with the people of that country.
● If their total fasts add up to 29 days, nothing is required of them.
● However, if they have only fasted 28 days, they must make up one day after Eid, because an Islamic month cannot be only 28 days.
How do I deal with whispers (waswasa) in ablution and purification?
Whispers in ablution are from Satan, and the Muslim should not pay attention to them. He is not required to re-perform ablution or repeat washing a limb because of waswasa. He should always base his purification on its being valid. It is recommended for him to frequently say "La ilaha illa Allah" (There is no god but Allah), because Satan recoils when Allah is mentioned. And Allah the Almighty knows best.