Help imobilizer light flashing

Went shooting last night,car ran sweet as a nut down to my permission 25 miles, but when driving round off road the engine and imobilizer lights stared flashing and the Rev counter needle bounced around and the power was lost.Happened twice so we left it for 30 minutes before driving it home with no problem.Took it out this morning and again after about 30mls same thing.called breakdown who hooked it up to diagnostics and there was no codes stored,so it got brought back to my local garage on a flatbed.
Been googling and there is loads of threads on this but no fixes,any ideas? Left it with my local garage for now but don't know if they can sort,poss need to take it to Suzuki.Strange this is that when this problem doesn't occur it runs and ticks over beautiful.

Sounds like a cam or crank sensor issue.

That's what's comming up on most of my searches,the breakdown guys diagnostics got no codes,so hoping my local garage can pin point( none Suzuki ).If not I think I will have to get it into a Suzuki dealers
It's a M13A engine

M13a engine? Probably crank sensor behind the alternator. Easy swap 1 10mm bolt and one connector. Just fit a new one Dave on garage fees. Garage won't be able to check it unless they take it for a run. You could always try the trick of cooling it with water as soon as it does it (the sensor) to pin point that is your problem.

And with a sensor problem you rarely get codes captured

Thanks lads just waiting for a call from garage,the breakdown guy got no codes so hopefully it's only one of the sensors,might just get the garage to go ahead and change both.