I would just tighten up your table selection a lot. This will increase your win rate and decrease your variance. Perhaps try only playing non-full stack players who don't have auto rebuy on~

Take a short break, go for a hike / long run, forget about poker for a while (can be only 24 hrs, as long as you're disiplined enough to accept you need to reset your mind, and indeed freeing yourself from poker).

After having taken that distance, come back to the game with a little work, review some hands, watch a video, watch some HU play on youtube even, whatever. Just anything that can give you passion, interest in the game. Watch some masters of poker making incredible folds, and being very confident about themselves.

Come back to play, keep your focus, crush.

All of this is mind training, and energetic management (you need to reset sometimes, otherwise you just insta-tilt for no reason). Don't expect to master the toughest part of the game in one week though ;).

I understand how you feel, I went on my 2 biggest downswings of the year just last month. But from what I have been able to tell 10 to 20 BI downswings are fairly common even at 6 max, I think the main reason mine are usually smaller is I play on the U.S. sites but if you play stars I don't think 17 buy in downswing is something to be overly concerned with. For sure, I wouldn't make any major changes to your game during this time. Instead, I would focus my energy in improving my mental game and knowing that when you are tilting to quit....it is not a race, you don't have to play x amount every day, but as your mental game improves you should be able to play those x amount of hands more often, whatever it is you would like x to be.

You are in for a rough ride with poker if you think 17-BI is a big downswing...

I'm now down around 30BIs in SNGs though managed to recover some in cash games but I can't grind anymore. I keep tilting after constantly breaking even or losing 4-5 BIs. I run bad and I play bad, keep making frustation calls when I know I'm beat. I just need to get back where I was able to play 8+ hours and constantly playing well.

Need help..

Get a book that deals with the mental game, such as 'The Mental Game of Poker' by Jared Tendler...i think there's a new edition that came out recently. I got the audio book a few years back. It's really good, especially the stuff on Tilt, the different types of tilt, what causes it, etc...(I had/have Injustice and Entitlement tilt...and have to keep working at it)

I used to grind HU SNGS and quit them after the last big downswing when I realized i couldn't handle the swings and variance and the tilt that was being induced. HU SNGS take a lot of mental fortitude and objective thought to be able to analyse your play and be honest about the upswings/downswings and break even periods. Knowing when it's run bad or bad play. I know this is true with all poker disciplines but i think HU SNGs are a beast unto themsleves. Calling too often when you 'know you're beat' is a sure fire sign of tilt that needs to be addressed. Give yourself a chance, work on your mental game...get a book...there's others out there, i just mentioned the one I own...but get to work on it if you're keen to be grinding full time. 

In times of trouble, focus your energy on withdrawing from the fight. It takes effort to withdraw ; can be taking a break, but not only, it's actually removing yourself from the equation. Find ways to appease your mind.

It's not easy to take breaks effectively, but that is one key to poker success. Managing bad times is what makes the difference between pros and the rest of the winning players.