In case you don't know, we are fasting the 9th, 10th and 11th of Muharram, the 1st Islamic month of the year. We fast these three days to have all our sins forgiven and to not mimic the Jews who will be fasting on the 10th alone.
If you cannot fast all three days, fast what you can. Make your silent intention and if something prevents you from fasting such as illness, your intention will grant you the blessing of a fast you missed.
It is a time when great joy will be bestowed on you. Don't miss this blessed time.