sudden

(all) of a sudden

suddenly

突然地

I feel really tired all of a sudden.

我突然間感到真的很累。

on a sudden

archaic way of saying all of a sudden

(古)。 同 all of a sudden

all of a sudden

Very quickly and unexpectedly; suddenly.

突然地：非常迅速地和突然地；出乎意料地