überfallen
to attack
To attack someone suddenly and unexpectedly, often with the intention of robbing them.
Die Bank wurde am helllichten Tag überfallen.
The bank was attacked in broad daylight.

to attack / overwhelm
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to attack
To attack someone suddenly and unexpectedly, often with the intention of robbing them.
Die Bank wurde am helllichten Tag überfallen.
The bank was attacked in broad daylight.

'Überfallen' (to attack / overwhelm) is an inseparable verb. The prefix 'über-' always remains attached to the verb and is not placed at the end in main clauses. The stress is on the second syllable: über-FAL-len.
Gestern überfiel ein maskierter Mann die Tankstelle.
Yesterday, a masked man attacked the gas station.
Because 'überfallen' (to attack / overwhelm) is an inseparable verb, the past participle is formed without the prefix 'ge-'. The correct form is 'überfallen', not 'übergefallen'.
Er wurde auf dem Heimweg von zwei Männern überfallen.
He was attacked by two men on his way home.
You can distinguish the meanings by the subject of the sentence. If a person is the subject, it usually means 'angreifen' (to attack) or 'überrumpeln' (to catch someone off guard). If a feeling or state, such as tiredness or fear, is the subject, it means 'überkommen' (to come over / overwhelm).
Der Täter überfiel sein Opfer von hinten.
The perpetrator attacked his victim from behind.
When a feeling or state 'überfällt' (overwhelms) someone, that feeling is the subject of the sentence. The person experiencing the feeling is in the accusative.
Nach der langen Wanderung überfiel uns ein großer Hunger.
After the long hike, a great hunger overwhelmed us.
to surprise
'überraschen' and 'überfallen' have in common that something comes suddenly and unexpectedly. But 'überraschen' is much more neutral and can also be positive. 'überfallen' is stronger and usually negative: it can mean an attack, but also a very sudden visit, an unpleasant question, or a strong feeling that comes on suddenly. Learners may confuse the words because both emphasize the unexpected. As a guide: 'überraschen' fits normal unexpected situations; 'überfallen' sounds like pressure, an attack, or a very strong sudden effect.

Nach der Arbeit überfällt sie plötzlich große Müdigkeit.
After work, she is suddenly overwhelmed by great tiredness.
Ihr überrascht mich mit euren guten Ideen im Kurs.
You surprise me with your good ideas in class.