Helping students is what they're paid to do.
I personally don't like this attitude. Maybe i've read it in the wrong way. They are there to help everybody, not bow down to you and jump through hoops just because you are terrified of them. A school teacher on average has 3-4 (maybe more) classes if they are full time. While it is correct they are there to help and guide, they cannot make you like them or respond to them in a different way. Teachers are humans too and obviously if we liked and could easily communicate with/appreciate everybody, the world would be a much better place. Sadly, this isn't the reality and we are going to come across people in our life that are easy to get along with and others that aren't.
In regards to your actual question now: The teacher realistically should be approachable particularly at VCE, so ask yourself why you're "terrified" of them. The teacher is your go-to person for that discipline, so if you're terrified of them then this is an individual thing where you need a resolution. Tbh the best way of approaching this is having a chat to them outside of class and voicing your concerns. The relationship between teacher and student at any year level is important, but arguably the most in Year 12. You will find that 99.9% of teachers are reasonable when they're made aware of these feelings and they will go above and beyond to try and help whereever they can. Teachers are not mind readers and cannot sense that you are 'terrified' of them and are unwilling to ask for help.
As an alternative, you can approach another teacher who teaches the same subject at your school but i'd be hesitant in doing this just incase your teacher gets the wrong idea. I don't think most would care and would take the view that it's good you're independently seeking help from another source... but you may get that odd one out.
Finally as an additional alternative, I have seen situations where the relationship is fractured and somebody in student management conducts a mediation (different wording probs) where the teacher and student work through any concerns with the aim of repairing the relationship.
(Obviously you can also seek other forms of learning e.g. videos, peers, somebody you do feel comfortable asking etc.. but I feel this is common sense so didn't include it in detail.)
Have you ever voiced these concerns to your teacher (or somebody else) or is this the first time (posting on here)?
And what if you have to wait a century before they reply to their emails, but by that time it's too late?
Again, this attitude I don't like. Let me just address this and say that teachers are not required to respond to emails outside of their school day and outside their 38 hour working week. We already do an absolute ton outside of the regular school time boundaries which you may not be aware of. Like I have stated, a regular teacher who works full time will have 3-4 classes of ~25 students.. if you send an email and don't get a reply within a reasonable time, it is your responsibility if you want the assistance urgently, to go and seek it.
I would assume that your lessons are spread out over the week for a given discipline (perhaps chunked together in 1-2 days even), which still provides ample opportunity to address your questions face-to-face if you were willing to.