Fundamental decisions 1

Before we can consider problems of everyday life, such as synthetic biology or computational chemistry, we have to solve some fundamental problems.
The first question is that of reality: Do we live in a place called reality, is this reality something external or internal, or do we live in a simulation, either a gigantic, universal, external one, or are we the only one in the simulation (that should be said in another way: Am I the only one in this simulation).
How can we start to think about that without going mad? I guess a lot of people have considered this question more or less systematically.
We leave the question of a maker of this reality and about the guys who run the simulation aside for a while.
a) The real exists and is external to us:
Ha: Even if we are in a simulation, there has to be some place real where the simulation is run, even if it is a black hyper-intelligent blob at the end of another parallel universe. So that is nice indeed. Even though our minds are distorted by thinking and by weird heuristics, we regularly bump into things, which means: There is something out there. All the materialistic and empiristic traditions bring us to a real world. It is only a problem of our senses, to get it right.
b) The real exists but is only in our minds:
A tricky one, that I have never fully understood. I miss the social component in this and especially the things we regularly bump into. A shared universe should be external to us. But the trick is that the only way to know the world is with our senses and our mind. That makes us alone, and unique spectators of the universe. Another nice aspect, I can live with.
c) We are in a huge simulated universe
Nice technology, I would say. Especially the sensation of bumping into things, is done really perfectly.
I guess it does not make a difference, except maybe possible afterlives, but that is another issue.
d) I am the only one in this simulation
Still rather nice technology, given the complexity, that I experience. Especially the error messages that frequently pop up above, add to the realistic feeling. Well done. I guess if I get out of this I either wake up in a tank full of liquid, wired to whatever, or I have 8 legs and look insect like.

I hope to have the time to read some philosophical ideas about all that.