Since it was you who got sick, why did you say " mum is afraid of being/getting ill/sick"? . According to meaning, 'mum' is the subject of 'being ill'. It didn't sound reasonable. 怕病 is just as 'be afraid of illness', also, it sounds unreasonable scared/afraid of being/getting ill/sick---怕'生'病. '生' is like 'getting'

1) you can say someone is 怕病(well in china we did say 怕生病)。and everyone corrected you because you add a followup我在楼上待了一天. you did say everyone said因为妈妈怕我生病; 因为妈妈怕我会生病, 我的病会加重.in chinese,你在楼上待了一天，是因为你妈妈怕你生病了（it's you getting sick）。你想表达的是你妈妈 is afraid of being/getting ill/sick herself.but with that last sentence,we automaticlly thought you were saying your mom is afraid that you will get sick. 2) 怕病= afraid of sickness. sickness is a thing,a fact,there's no need to be afraid of.it's not like snakes.you can say 我怕蛇，蛇is an actual animal。 我怕热，热和冷相对，hot cold.而“病”本身是没有两面。只有getting sick and getting cure 生病和不生病。所以我们说怕生病。

妈妈怕病 means "Mum is afraid of sickness." But people cannot touch or see sickness. They can only get sickness. Thus, few Chinese people say 妈妈怕病. Instead, they say 妈妈怕得病/妈妈怕生病 which means "Mum is afraid of being sick".

妈妈怕病=Mom is afraid of illness. 妈妈怕生病=Mom is afraid of getting sick. English speakers say "get" sick. The Chinese speakers say "生“= produce, hence, 生病=produce sickness (noun) = get sick (adjective) . English speakers say "give birth", while the Chinese say "生孩子”. To say "she is about to give birth" in Chinese would be :"她快生了“。

look, this is why all of people say the chinese is the hardest language.......... for your questions like this, I can just say: no rule, it is just like this... what you can do is just remember them.......... we just say someone 害怕/怕 得病/生病 we NEVER say someone 害怕/怕 病 EVEN I know there is no grammar-fault..... if you really need an explanation, I can just say: beacuse all chinese people say 害怕生病 NOT 害怕病.......:D