Is this a hyperbole: "Reminiscing, taking a deep dive into the sea of memory."?
This statement is metaphoric. A hyperbole is basically an exaggeration, and there isn't anything exaggerated in this sentence. An example of a hyperbole is ' enough food to feed a whole army '
A metaphor on the other hand is more of a symbol.
The Merriam Webster Dictionary states:
"[a metaphor is] a figure of speech in which a word or phrase literally denoting one kind of object or idea is used in place of another to suggest a likeness or analogy between them (as in drowning in money"