I'm absolutely sure

I learned how to say things with confidence.

I'm (absolutely | 100% | pretty | fairly ) ( certain | sure ) ...

Other phrases to show confidence:

• probably (50% - 60%)
• maybe
• perhaps (50%)

Could, might and may are also used to show confidence:

• could (have | be)
• might (have | be)
• may (have | be)

All of a sudden

I learned phrases following:

• When all of a sudden the building began to shake, some of people screamed.
• We got out just as the building was about to fall down.

I found an interesting video clip when to search "a goner."

Oh, that reminds me of the time ...

I learned phrases at my english class yesterday.
Those phrases are to say about what I used to do remembered by someone's story.

Oh, that reminds me of the time ...
 I must have been 12 at the time.
 Anyway ...
 It was ...

For example,

Oh, that reminds me of the time when I first went to the kindergarten.
 I must have been 4 at the time.
 Anyway, I kept crying for a while after my mon had gone.
 It was an unforgettable event.