Truly; certainly (synonyms for really?)

Hi teachers,
Would, ‘truly; certainly’ be appropriate synonyms for ‘really’ in the following examples?
I know ‘truly’ is, let’s say, the natural one. But, could ‘certainly’ be also possible?

A: Now I really must go home.
A: Am I really wonderful?

Thanks in advance.

*** Not a teacher ***
I would take you first example as falling within that definition: “used for emphasizing what you are saying about a situation
I really must settle down to some serious work. There’s really no need to worry.”
– It’s closer to “Now I do have to go home” as it appears, than to “Now I certainly must go home” (implying “Having done all I did”.
Your second example seems to be in line with: “usually in negatives or questions] completely
Are you really sure that you want to marry this man?
It isn’t really a dictionary – it’s a sort of phrase book.”
–Would be interesting to here from the others…

Sorry Eugene but I could not really understand your explanation very well. I think you can substitute certainly for the first sentence with little change in meaning but it does not work for the second sentence.

But I didn’t try to substitute ‘certainly’ for either of the sentences, Luschen.
Conversely, I was trying to prove it doesn’t fit in with the examples bearing different meaning.
My take on it: 1) sounds along the lines of “Now I do have to go home”
2) ~Am I completely wonderful?
What do you think?

Hi Eugene. Sorry now your response makes perfect sense. I must have read it too early in the morning. I do disagree with your analysis of the second sentence. I think really is used to express doubt and asking for confirmation of something the speaker doubts or thinks is not true.

Do you really think English is easy to learn?

Do you really like my new haircut?