All perfect praise be to Allah, The Lord of The Worlds, and may His peace and blessings be upon our Prophet Muhammad and upon all of his family and companions. 

Whoever vowed to perform an act of devotion and couldn’t recall it, is obliged to make Ijtihad (Independent reasoning) regarding it, and tries as much as possible to specify the closest clue to his vow, but if he couldn’t, then he is obliged to perform all acts of devotions that he is confused with in order to be on the safe side.

Besides, Ibn Hajar Al-Haythami (May Allah have mercy on his soul) said (What means): ”If a person made a vow and was conditioned to be fulfilled after being healed, but couldn’t recall which act of devotion that has to be fulfilled according to the vow; whether it was giving charity, manumitting of salve, fasting or performing prayer, then and in accordance with the Shafie’s doctrine, it is more prudent to make Ijtihad (Independent reasoning), but if he did this and couldn’t determine which act he vowed to perform, then he is obliged to perform all acts of devotion that he is confused with because he won’t be free from the liability save by performing all of them, since what accomplishes an obligation is an obligation.”. [Tohfat Al-Muhtaj vol.10 pp. 75].

In conclusion, you (Questioner) are obliged to fast 10 days and perform 10 Rakas in order to be free from the liability. And Allah Knows Best.