There is no sin on a person who drops the Mus-haf unintentionally
Praise be to Allaah.
No Muslim doubts that it is obligatory to respect the Book of Allaah, and the scholars are agreed that the one who deliberately mishandles it is a kaafir.
At the same time, Allaah says that there is no sin on one who is ignorant, forgetful or makes a mistake.
Allaah describes the believers as saying (interpretation of the meaning):
“ ‘Our Lord! Punish us not if we forget or fall into error’”[al-Baqarah 2:286]
According to a report narrated by Muslim from the hadeeth of Abu Hurayrah (125), Allaah said. “Yes”; according to another report from the hadeeth of Ibn ‘Abbaas (126), Allaah said, “I have done that” (i.e., responded to the prayer uttered in this aayah).
Whoever has no free will in a matter, such as one who is forced to do something, or one who is asleep, is not sinning if he says or does something that goes against Islam.
You have not done anything that goes against Islam. When the Mus-haf fell it was not by any deliberate action on your part, so you have not fallen short in respecting it. Although Islam tells us that we must repent from our sins and give them up, at the same time it warns us against falling prey to waswaas (insinuating whispers of the Shaytaan) and despairing of the forgiveness and mercy of Allaah.
We ask Allaah to help you to do that which He loves and is pleased with. And Allaah knows best.