I want to know the exact meaning and difference between SHIFA'ah and SHAFA'ah and which one we need to ask Allah for?
In Arabic, words are made up of 2 or more consonant letters, collectively called as Root Words.
Vowels are changed to express tenses.
and hence mean the same.
The second part of the question is answered by Andre and I support it.
You want Allah's mercy to intercede on your behalf and forgive you for the sins you are regretful for.
May the creator guide us all.
means intersession. Intersession is when someone intercedes/intervenes on your behalf.
So you should ask Allah for SHAFA'ah as well. You want Allah's mercy to intercede on your behalf and forgive you for the sins you are regretful for.
We can also ask Allah for the intercession of the Prophet and the great Saints (such as the family of the prophet).
For example people make a prayer such as this"
By the Right of Muhammad and His Pure household, Oh Allah please forgive me, my parents and my family!
This is called Intercession, Tavassol, Shafaat.
Shifa is Allah's intercession / permission for the granting of a healing or Allah's will grant whom he wills the permission to intercede for the forgiveness of our sins as stated in the Versee of the Throne " none shall intercede for you save by Allah's permission". So in my mind shifat / Shafat (I agree the similarity as commented in a prior answer) would have two contexts 1) for intercession for healing from physical sickness and 2) intercession for the the forgiveness of sins you acknowledge or are aware or unaware commited yourself current disbelief in Allah or ascribing partners to Allah who knows and guides best!
Shifa means "good health"
Shafa means "corner, death, deep grave"
So you should ask for shifa from Allah. Allah knows what's going on in your head and heart, so if you are asking for good health but due to lack of knowledge you use the word Shafa (as actions are based on intention) I don't think you need to worry as your intention was to ask for good health. Allah knows best.