1) Breathless 2) Dyspneal 3) Dyspneic 4) Dyspnoeal 5) Dyspnoeic 6) Smothering 7) Suffocative 
• a. & n. from Suffocate, v. • (p. pr. & vb. n.) of Suffocate
Suf'fo·ca`ting adjective & noun from Suffocate , v. -- 
suffocating 1. To kill or destroy by preventing access to air or oxygen. 2. To impair the respiration of; asphyxiate. 3. To cause discomfort to by or as if by cutting off the supply of fresh air. 4. To suppress the development, imagination, or creativity of; to stifle; such as, `The rigid formality of the place suffocated her.” 5. To die from...
causing difficulty in breathing especially through lack of fresh air and presence of heat