
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.

to spring on
To confront someone unprepared with a visit, question, or task; to catch someone off guard.
Entschuldigung, ich wollte dich mit meiner Frage nicht so überfallen.
Sorry, I didn't mean to spring my question on you like that.

to overwhelm
Feelings, tiredness, or thoughts that suddenly and intensely come over someone.
Nach dem langen Tag überfiel ihn eine bleierne Müdigkeit.
After the long day, a leaden tiredness overwhelmed him.
'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
Both verbs can describe an unexpected encounter or confrontation. „Überraschen“ neutrally indicates that someone did not expect something. „Überfallen“ sounds much more forceful and can have an aggressive effect, even when referring to a sudden question or task. For an ordinary unexpected piece of news, „überraschen“ is therefore the better choice.

Die Reporterin überfiel den Minister vor laufenden Kameras mit einer unerwarteten Frage.
The reporter sprang an unexpected question on the minister in front of the cameras.
Die Reporterin überraschte den Minister mit einer unerwarteten Frage.
The reporter surprised the minister with an unexpected question.