Synonyms for Suffocating (same or very similar meaning)
WordNet sense 1 (causing difficulty in breathing especially through lack of fresh air and presence of heat):
smothering, suffocativeWordNet sense 2 (not breathing or able to breathe except with difficulty):
breathless, dyspneal, dyspneic, dyspnoeal, dyspnoeicFrom the ODE community, based on WordNetadd/edit