"Tousled" is nearly always used to describe hair. "Dishevelled" may refer to hair but also clothing or general appearance. Tousled hair *may* be fashionably messy hair (now). A mother might affectionately tousle her child's hair. Dishevelled hair (or clothing)is the result of lack of care/grooming or a sign of recent activity.

Yes, you could describe your hair as disheveled, tousled, scruffy, unkempt, ungroomed, bedraggled, mussed, disarranged, straggly, untidy, messed-up...