There is a radio interview with Coverdale on the Whitensake 87 album where he talks about this...only for you, my lads, I've transcribved a little bit of it.

Basically, the recordings were going fine, and one day in his words, "I developed an appalling sinus infection which not only prevented me from singing in tune, but without any range at all. I started to sound very nasal, like I had a cold but I didn't. I didn't have the symtpoms of a cold, but I sounded like it. The first song I went in for was 'Is This Love'. I thought, 'I won't overdo it. Let's see'. And I sang the song from beginning to end, out of tune. And I couldn't tell. And at the end of it, I was dripping with sweat. I was exhausted, and that is not really an exhausting song to perform". They all take a break for a few weeks, but he keeps sounding more and more nasal. So he saw a doctor, who said it was the worse sinus infection he had ever seen and said he was surprised Coverdale could even talk.

So, he takes this really potent antibiotic for 6 weeks (Keflex or something like that)

He heads back to the studio after getting his clean bill of helath, flies down with Sykes and Mike Stone to the Bahamas. And a week later, the infection had flooded back in. So he asked Kalodner to temporarily pull the plug in the project. And they had to operate him for this sinus infection and collapsed septum with a 50/50 chance he'd never sing again.

Anyway, in the words of the radio guy and Coverdale himself:

Narrator:

Now, to add insult to injury, while David Coverdale wrestled with career-threatening throat surgery, his writing partner and guitarist John Skyes left! And producer Mike Stone suggested to the record company that they replace David Coverdale! Producer Stone was summarily fired.

Coverdale:
"I'm afraid I was the only Snake in residence! (laughs). One of the indications, I must say, I received absolutely no support from my partner, Sykes at that time. In fact, I was mortified that he did everything he could to take advantage of my being compromised. But, I must tell you, the only thing I can compare it with is castration. The idea of not being able to do it ever again, would really compromise the joy of...I tried as a thinking person to come to terms with the idea that I could still write, I couls till produce, and express myself through that, but of course somebody else would be singing my songs...It was a dreadful, dreadful, dreadful 86."

With a new producer, Keith Olsen, but no band, and maybe no voice after surgery, David Coverdale can never forget the first time he re-entered the studio to attempt to sing again:

"Well, I've gotta tell you...extremely nervous! Indescribably nervous. I mean, I, I don't think there's a word for it. Olsen was great! He said, "let's just have a couple of run-throughs". I said, "What do you want to start with?". He said, "Still of the Night". I almost vomited! "You can't be serious!".
He says, "I won't record it." And I sang the song twice, just fingers crossed - and that's what's on the record. It's a blend of two passes. And then he went, "I think we've got that one". And I - cause I thought I was just doing run-throughs, so there wasn't the psychological weight that I was going for it."

That's what I know.

Cheers,
Jack.