A great friend of mine coined the term 'Eish' which I use almost daily in my life. I have interpreted its sound into how I think it would be written.
I find the situations to use this word best fit when you are slightly shocked about something, or worried about something.
It is a 'gasp' as such, which represents the feeling of concern, but at the same time excitement.
I challenge you to use it in everyday life...Perhaps see if it catches on...
I believe it belongs in the dictionary...if the word 'LOL' can make it in the Oxford Dictionary so can 'Eish'
It can fit well in a text or in a conversation, and really sometimes just somes up a feeling which might normally take a sentence to express...off you go...use the word EISH!