Of course, Installing a horizontal tilting bed in a recess with concrete walls can be a feasible option. Given that the width between the walls is limited to 195 cm and you are considering a 120 by 190 bed, attaching the plates directly to the walls might be possible. The walls can indeed act as formwork in this scenario. However, it is essential to ensure that the walls are structurally sound and capable of supporting the weight and load distribution of the bed to prevent any safety issues. It is advisable to consult with a structural engineer or a professional installer to assess the feasibility and safety of this installation method.