那是个夸张的说法。 就是非常推荐的意思。meaning it's a super recommendation to see that post ..

吐血：一种生理现象，一般指病情严重，血由口中吐出，就是所谓的直到吐血甚至死亡。推荐：原义是推而荐之；单说，推：有向外，向上拱的意思。荐：古时候，有才学有能力的人，受到朝廷的臣子们以及官员的欣赏，由他们向皇帝引见的意思。现在不单指对人的举荐。只要好的，值得向人介绍的物品等都行。吐血推荐：粗俗的讲：就是到死那么厉害都要向人介绍的好东西或者人等。书面解释就是：强烈的介绍或者特别的介绍。

It means strongly recommend. eg. 阿凡达太好看了，我吐血也要推荐。

well,this phrase u can't find it in the school book,hehe,u just need to understand it literally,for me,as i'm a native chinese speaker,I also never check in in the dictionary for defination;but i think even for mandarin learner,u can understand it subconsciously. oh,if u think i speak rubbish,just give me a big thumbs down,hehe.