## 1 Introduction
Among them is increasing the patient motivation by providing an interesting and interactive environment; additionally, virtual reality is easy to modify, allowing rehabilitation to be tailored to meet the needs of a particular group of patients or even a specific individual. In addition, in some cases VR rehabilitation is available remotely, making it more accessible to patients, often reducing its cost. The use of virtual reality may have greater benefits in post-stroke patients in terms of balance, mobility, or walking speed compared to standard rehabilitation [30]. Speaking of VR applications, one can distinguish between immersive and non-immersive VR. Immersive VR allows for deeper interaction and \"immersion\" in the virtual environment [31]. Immersion is usually considered on a scale or along a continuum, from least immersive to fully immersive, and typically involves elements such as a continuity of surroundings, physical interaction, and 3D audio. This effect is achieved through the use of appropriate devices (most often head-mounted displays (HMDs)) and innovative software to create realistic visuals, smooth interactions, and unique experiences. All of this is designed to make the user feel as if they are in a virtual environment. Non-immersive VR systems rely on a computer or video game console, a display, and input devices, such as keyboards, mice, and controllers. In non-immersive virtual reality, users can control characters or actions in the virtual environment but the virtual environment does not interact with them directly [32]. Many more studies on the use of non-immersive VR have been described in the literature [22; 23; 30; 33; 34; 35]. The reason is that the availability of VR devices that allow deep immersion has been significantly reduced in previous years. Nowadays, due to the rapid development of head-mounted devices, immersive applications are gaining popularity. Thus, the advantages of using immersive VR over non-immersive VR is more realistic and fully immersive experiences, which can lead to a greater sense of presence and engagement. In addition, immersive VR can also be a more effective tool for learning and training, as it allows users to experience and interact with a simulated environment in a more realistic and engaging way [22]. But the use of virtual reality is also associated with risks: decreased visual-motor stability, which can have a detrimental effect on eye-directed motor skills, mental disorders manifested by not distinguishing between the virtual and real worlds [36], and cybersickness [37]. Problems with motor skills, in particular, manifest in complex precision movements such as throwing darts [38], where there were noticeable differences between those trained in VR and in reality. These differences were largely due to the mapping of the environment in VR and thus resulted in learning different movement patterns than those used in reality. According to studies [39; 40], varying degrees of severity of cybersickness symptoms have been reported in 22-80% of those using the technology. The symptoms of this disease are similar to motion sickness and occur during and after immersive VR use [41]. Symptoms include headaches, paleness, eye fatigue, sweating, fullness in the stomach, a dry mouth, disorientation, ataxia, dizziness, nausea, or vomiting [42]. Due to the possibility of cybersickness, it is essential to take this factor into account when developing the game, as well as when using it with patients. The purpose of this paper is to propose a new way of rehabilitating post-stroke patients with upper limb paresis or unilateral spatial neglect using a virtual reality application. The novelty of the created game is its immersiveness and focus on the rehabilitation of patients with USN syndrome, which will entail a number of advantages, as described below. The study presented in this article aims to expand the knowledge of the use of VR in medicine and rehabilitation, particularly post-stroke neurological rehabilitation.