Not only today but also rRecently, I alwayshave been feeling confused and disoriented.

"Not only today, but also recently" is redundant; you are saying the same thing twice.

You should also change the verb "feel" to present perfect continuous, because you started to feel confused and disoriented in the past but you also feel this way now.

I know that the most important thing for me is to finish my Ph.D. thesis, get my degree and then, go home, and look for a job.

But, the truth is that when I have a project, such as memorizing vocabulary, I can't concentrate.

Perhaps the most important thing was to washclear my mind and understand that slow is fast and fast is slow.

We usually say use the phrase "clear my mind" in these circumstances

Each day is a little bit better than the persoI am a slightly better person than I was yesterday.

Feeling confused and disorientated

Not only today but also recently, I always feel confused and disorientated.

Perhaps the most important thing was to washclear my mind and understand that slow is fast and fast is slow.

mind washing = brainwashing

Each day isI am a little bit better than the person I was yesterday.

Feeling confused and disoriented

Not only today but also recently, I always feel confused and disoriented.

or: I have been feeling

Perhaps the most important thing was to wash(is?) to clear my mind and understand that slow is fast and fast is slow.

“Wash my mind” sounds like brainwashing, which isn’t what you mean.

We (I?) still have a lot of time.

“We” seems odd, since you’ve been talking about yourself until this point.

I've lostmissed so many opportunities in my life beforthroughout my life.

“Missed” sounds more natural to me, if you’re talking about personal opportunities that have come up throughout your life.

Each day isI’m a little bit better than the person I was yesterday.

Feeling confused and disorientated

Not only today but also recently, I always feel confused and disorientated.

Perhaps the most important thing was to washreset my mind and understand that slow is fast and fast is slow.

Each day isI aim to be a little bit better than the person I was yesterday.