Study protocol for the Heads-Up trial: a phase II randomized controlled trial investigating head-up tilt sleeping to alleviate orthostatic intolerance in Parkinson's Disease and parkinsonism. - van der Stam AH; de Vries NM; Shmuely S; Smeenk D; Rutten JH; van Rossum IA; de Bot ST; Claassen JA; Bloem BR; Thijs RD (BMC neurology, 2024)