De huisarts verwees hem door nadat hij flauwviel.

Huisarts is the usual Dutch word for a general practitioner / family doctor / GP.

It is more specific than dokter:

• huisarts = your regular primary-care doctor
• dokter = any doctor in general

So in this sentence, de huisarts tells you that this is the patient’s GP, not just any doctor.

Because the verb is doorverwijzen, which is a separable verb.

In a main clause, Dutch usually splits separable verbs:

• De huisarts verwees hem door.

Here:

• verwees = the finite verb part
• door = the separable particle

In other forms, the parts often stay together:

• infinitive: doorverwijzen
• past participle: doorverwezen
• subordinate clause: dat de huisarts hem doorverwees

So the split is normal Dutch word order.

It means to refer someone on, usually to another doctor, a specialist, or a hospital.

So this is not just pointing him somewhere. It means the GP decided that the person needed further medical attention elsewhere.

That is why door is important: it adds the idea of being sent onward to the next level of care.

Because Dutch still distinguishes between subject and object pronouns here:

• hij = he as the subject
• hem = him as the object

So:

• De huisarts verwees hem door = the GP referred him
• nadat hij flauwviel = after he fainted

This works just like English he/him.

Grammatically, hij could refer to either masculine singular person mentioned earlier.

But in normal reading, it will almost always be understood as referring to hem, the patient:

• The GP referred him onward
• after he fainted

That makes the most logical sense.

If a speaker wanted to remove all ambiguity, they could say something more explicit, such as:

• De huisarts verwees hem door nadat de patiënt flauwviel.

That is another separable verb.

The infinitive is:

• flauwvallen = to faint

In a main clause, it splits:

• Hij viel flauw.

But in a subordinate clause, the parts join again:

• nadat hij flauwviel

So these are all forms of the same verb:

• flauwvallen = infinitive
• hij valt flauw = present
• hij viel flauw = past, main clause
• dat hij flauwviel = past, subordinate clause
• hij is flauwgevallen = perfect

Because nadat introduces a subordinate clause, and in Dutch subordinate clauses the finite verb normally goes to the end.

So:

• main clause: De huisarts verwees hem door
• subordinate clause: nadat hij flauwviel

This is a very common Dutch pattern:

• omdat hij ziek was
• toen hij thuiskwam
• nadat hij flauwviel

English does not move the verb to the end in the same way, so this is something English speakers often have to get used to.

Yes. The sentence uses the simple past in both clauses, which is very normal in everyday Dutch narrative style:

• De huisarts verwees hem door nadat hij flauwviel.

But Dutch can also use a past perfect to make the earlier action more explicit:

• De huisarts verwees hem door nadat hij was flauwgevallen.

That version emphasizes more clearly that the fainting happened before the referral.

So:

• flauwviel = natural and common
• was flauwgevallen = a bit more explicit about sequence

Both are possible, though the version with the simple past is very idiomatic.

Yes:

• Nadat hij flauwviel, verwees de huisarts hem door.

That is completely correct.

When the subordinate clause comes first, it takes the first position in the sentence, so the finite verb of the main clause still comes second:

• Nadat hij flauwviel, verwees de huisarts hem door.

Notice that you do not say:

• Nadat hij flauwviel, de huisarts verwees hem door.

Dutch keeps its verb-second pattern in the main clause.