A 22-year-old drama student lives in constant fear that an extreme form of asthma will kill her, as the slightest exertion can leave her bedridden and breathing "as if she is underwater" with "an elephant" sitting on her chest.Just 17 when she was diagnosed with brittle asthma - a severe, little understood and sometimes life threatening form of the incurable lung condition - Tabatha Ketteringham can be bedbound for up to two weeks a month and needs a mobility scooter to get around.Tabatha, of Wells, Somerset - who is studying drama at Bristol University and aspires to become a special needs drama therapist - is also scared that it will stop her from achieving her dreams, saying: “Some days, I’m not able to even put my shoes on, walk up the stairs, or have a shower, because it leaves me completely out of breath.