Human Activity Recognition (HAR) is a rapidly evolving field with the potential to revolutionise how we monitor and understand human behaviour. This survey paper provides a comprehensive overview of the state-of-the-art in HAR, specifically focusing on recent techniques such as multimodal techniques, Deep Reinforcement Learning and large language models. It explores the diverse range of human activities and the sensor technologies employed for data collection. It then reviews novel algorithms used for Human Activity Recognition with emphasis on multimodality, Deep Reinforcement Learning and large language models. It gives an overview of multimodal datasets with physiological data. It also delves into the applications of HAR in healthcare. Additionally, the survey discusses the challenges and future directions in this exciting field, highlighting the need for continued research and development to fully realise the potential of HAR in various real-world applications.