When you ask questions, it usually helps to give plenty of context. In other words - a few sentences either side of the quote, or a description of the scene. Without context, it is impossible to tell. So - I had to look up the quote for you. "What my sensations were no language can describe; but just as they all rose, stifling my breath and constricting my throat" The answer is 'sensations'. The sensations felt like they 'rose' from her stomach, and up into her lungs and throat, which made her feel like she could not breathe any more.

More context is needed to confirm this.