The original meaning of the transitive verb かける is like "(let) hang". e.g. 壁に絵をかける (let a picture hung on the wall). This "hang (in the air, not completely stabilized)" meaning has turned to mean "just started", "is about to start", or "not yet finished". 失いかける - be about to lose / almost lost ( not yet lost, it is still in your hands) 読みかけの本 - a half-read book. (not read through) 話しかける - say something to start the conversation. (not yet in the main part of conversation). 言いかけてやめる - say a little and stop there. (The sentence is not completed) 眠りかけていた　- almost got into a sleep (but now woken up). 失いかける　=　失い＋かける　（失い is the 連用形 of 失う） 失いかけた: the so-called past tense of 失いかける

いま見たら質問に-1がついていました。質問内容は妥当であり、-1されるべきではありません。私の方で+１して元に戻しました。 -1をつけた人へ＞ 人の意見に安易に-1をつけるのはやめましょう。匿名性を濫用した、はずかしい行為です。 I found someone downgraded the question, which I think is an inappropriate action. So I upgraded to resume it. To the anonymous and unfair downgrader> You may want to refrain from downgrading someone's question the content of which does not deserve it. It is an uneducated thing to do.

失い／かけ／た。 失い（conjugation of a verb "失う", which means "lose"）／かけ（conjugation of another verb "かける", which means "be about to do something" or "almost do something"）／た（particle which means that something happened in the past）／"失いかけた" means that you almost lost something.

It means something is about to/on the verge of ~. For example, 私は意識を失いかけた will be "I almost lost consciousness"