Self teaching Higher Physics

If you're comfortable with manipulating formulae and basic trig (SOHCAHTOA) you could get by. You might need to look up things like ohm's law, behaviour of thermistors/resistors (light up resistance down, temperature up resistance down (LURD and TURD)), some basic knowledge about nuclear decay for Unit 3 and other bits and bobs. The electronics in Unit 2 might require quite a bit of your time because you will have to learn from scratch how to do voltage divider calculations and details about transistors. Overall, there isn't TOO much you will have missed having not done the Standard Grade. if there's something that you don't know about because of this, you can always ask your teacher.

Provided you put in the effort and get issues ironed out ASAP you should be fine!

CallumFR is correct. You might want to spend a couple of weeks before you start going over the Standard Grade topics on electricity and electronics: BBC Bitesize is probably adequate in that regard. Provided that your Higher resources are good (the revision guide published by P&N is fantastic for learning the material if used alongside a book of exercises and problems, which you'd have no problem getting a hold of), you're unlikely to find the course difficult.

As a word of warning, I strongly recommend you avoid the How to Pass book for the course. It rarely seems to touch on content above grade C, the explanations are lacking and the questions are overly simple.

Enjoy!

There's a reason it's called how to pass

That said, completely echo what Oogamy And CallumFR have been saying. Would also add that towards the end of the year, you should get a hold of numerous past papers and do them all to find out any details you may have missed (this works well even if you aren't self teaching and have just forgotten )