خَرَجْتُ فَإِذَا زَيْدٌ
I went out, and suddenly there was Zayd.
«خَرَجْتُ» consists of a verb and its subject. Here «إِذَا» marks a sudden encounter. «زَيْدٌ» can be analyzed as a nominative subject with an understood predicate such as «حَاضِرٌ» (“present”), «مَوْجُودٌ», or, with suitable contextual evidence, a locative phrase such as «بِالْبَابِ».
An illustrative reconstruction is خَرَجْتُ فَإِذَا زَيْدٌ حَاضِرٌ.
The suddenness particle shows an unexpected occurrence, but it does not determine the exact location or quality of Zayd. One must not promote a convenient guess into a certain reconstructed word. Brevity reinforces the abrupt perception of the event.