Acostarse vs. tenderse vs. tumbarse vs. echarse

The Spanish verbs 'acostarse', 'tenderse', 'tumbarse', and 'echarse' all refer to the action of getting into a horizontal position, or 'to lie down'. However, they are used in slightly different contexts and thus, carry subtleties in meaning.

Acostarse

'Acostarse' is generally used to refer to 'going to bed' or specifically lying down with the intention of sleeping.
Voy a acostarme temprano porque estoy muy cansado.
(I'm going to go to bed early because I'm very tired.)
Acuéstense, niños, es hora de dormir.
(Go to bed, children, it's time to sleep.)

Tenderse

While 'tenderse' can also mean 'to lie down', it often carries with it a sense of spreading out or stretching out on a surface.
Puedes tenderte en el sofá y ver la tele.
(You can stretch out on the sofa and watch TV.)
Se tendió en la arena para tomar el sol.
(He laid out on the sand to sunbathe.)

Tumbarse

'Tumbarse' generally refers to the act of lying down without any particular emphasis on intent or position.
Me voy a tumbar un rato en la hamaca.
(I'm going to lie down for a while in the hammock.)
Después de comer, le gusta tumbarse en el sofá.
(After eating, he likes to lay down on the couch.)

Echarse

'Echarse' also means 'to lie down', but frequently implies doing so in order to rest or avoid doing something else.
Echémonos un rato antes de continuar con el trabajo.
(Let's lie down for a while before continuing with the work.)
Se echó en el césped para descansar después de correr.
(He lay down on the grass to rest after running.)

Summary

'Acostarse', 'tenderse', 'tumbarse' and 'echarse' all translate as 'to lie down' but are used in slightly different situations. 'Acostarse' is typically used when referring to going to bed or intending to sleep; 'Tenderse' implies spreading or stretching oneself out (often in contexts such as sunbathing); 'Tumbarse' is more general and simply refers lying down without specifying details; Finally, 'Echarse' involves lying down typically for resting.