An adjustment mechanism for a seat, the adjustment mechanism comprising: multiple screw shafts (111, 112; 211, 212, 213, 214, 215; 311, 312); a motor (150; 250; 350) for driving the screw shafts (111, 112; 211, 212, 213, 214, 215; 311, 312); and a clutch mechanism (160; 260; 360) for selectively engaging the motor (150; 250; 350) with one or more of the screw shafts (111, 112; 211, 212, 213, 214, 215; 311, 312); whereby a rotation of one or more of the screw shafts (111, 112; 211, 212, 213, 214, 215; 311, 312) caused by the motor (150; 250; 350) can translate into adjustment of the seat according to a first degree of freedom and a rotation of one or more others of the screw shafts (111, 112; 211, 212, 213, 214, 215; 311, 312) caused by the motor (150; 250; 350) can translate into adjustment of the seat according to a second degree of freedom, characterized in that the first degree of freedom corresponds to displacement of a headrest of the seat in a horizontal direction or to tilting of the headrest and the second degree of freedom corresponds to displacement of the headrest of the seat in a vertical direction; wherein the multiple screw shafts (111, 112, 113) comprise at least one first screw shaft (111, 112) and at least one second screw shaft and the adjustment mechanism comprises at least one nut element (121, 122) engaged with the at least one first screw shaft (111, 112), whereby a rotation of the at least one first screw shaft (111, 112) caused by the motor can translate into a linear motion of the at least one nut element (121, 122), and whereby in a first range of the linear motion of the at least one nut element (121, 122) the linear motion can translate into adjustment of the seat according to a one of the first degree of freedom and the second degree of freedom and in a second range of the linear motion of the at least one nut element (121, 122) the linear motion can translate into adjustment of the seat according to a third degree of freedom; and wherein the headrest comprises at least one flap element (52, 53) which is pivotable with respect to a main portion of the headrest and the third degree of freedom corresponds to pivoting of the at least one flap element (52, 53) with respect to the main portion of the headrest. multiple screw shafts (111, 112; 211, 212, 213, 214, 215; 311, 312); a motor (150; 250; 350) for driving the screw shafts (111, 112; 211, 212, 213, 214, 215; 311, 312); and a clutch mechanism (160; 260; 360) for selectively engaging the motor (150; 250; 350) with one or more of the screw shafts (111, 112; 211, 212, 213, 214, 215; 311, 312); whereby a rotation of one or more of the screw shafts (111, 112; 211, 212, 213, 214, 215; 311, 312) caused by the motor (150; 250; 350) can translate into adjustment of the seat according to a first degree of freedom and a rotation of one or more others of the screw shafts (111, 112; 211, 212, 213, 214, 215; 311, 312) caused by the motor (150; 250; 350) can translate into adjustment of the seat according to a second degree of freedom, characterized in that the first degree of freedom corresponds to displacement of a headrest of the seat in a horizontal direction or to tilting of the headrest and the second degree of freedom corresponds to displacement of the headrest of the seat in a vertical direction; wherein the multiple screw shafts (111, 112, 113) comprise at least one first screw shaft (111, 112) and at least one second screw shaft and the adjustment mechanism comprises at least one nut element (121, 122) engaged with the at least one first screw shaft (111, 112), whereby a rotation of the at least one first screw shaft (111, 112) caused by the motor can translate into a linear motion of the at least one nut element (121, 122), and whereby in a first range of the linear motion of the at least one nut element (121, 122) the linear motion can translate into adjustment of the seat according to a one of the first degree of freedom and the second degree of freedom and in a second range of the linear motion of the at least one nut element (121, 122) the linear motion can translate into adjustment of the seat according to a third degree of freedom; and wherein the headrest comprises at least one flap element (52, 53) which is pivotable with respect to a main portion of the headrest and the third degree of freedom corresponds to pivoting of the at least one flap element (52, 53) with respect to the main portion of the headrest.