Verbs that point back to the one performing a task are called reflexive verbs. Examples for this type of verb are “He washes himself”. He’s not washing Haley or Jim or his dog but only himself. You notice this when you see the little word sig (spoken sej). This pronoun is used for he, she, and it. Han, Hon, and det. All other persons use their corresponding object pronoun like mig, me, and dig, you.
The first group contain the words that are ALWAYS reflexive. They cannot stand without this pronoun because the subject cannot perform this task on anyone else.
De har förlovat sig.
They’ve got engaged.
Paret har förälskat sig.
The couple has fallen in love.
This second group contains the verbs that really aren’t reflexive at all but when the subject is doing them to himself they automatically become reflexive and the reflexive pronoun has to be used.
Han tvättade hunden.
He washed the dog.
Han tvättar sig.
He washes (himself).
Both Swedish and English have reflexive verbs, as do a bunch of other langauges, but mostly they aren’t the same. This is just a matter of linguistic evolution and has to be learned.
Reflexive in Swedish
Reflexive in English
There really are no verbs in English that are reflexive only. All belong to the second group and for words like to wash, to shave, and to dress the reflexive pronoun is mostly omitted.