Starting up: expect lots of discomfort. There's so much bigCo support you have to re-build and it is hard to hire. It might be better to spend 6mths - 1yr at A/B stage co first then only to the founder stage. Alt, try doing something on the side to begin with. Find a partner in crime.

L7 & single? You can afford to pay the outside co-founder a bay area survivable amount (140-200 varies) and have that person work through some of the early situations and then skip out when things are moving along (eg. think A round). Risk-adjusted & safe but yet keeps a lot of the upside while allowing you to taste what it's actually like.

L8? Risk-reward ratio is skewed towards staying at a FAANG. Find and fund a few projects. See what happens. Get excitement outside of work (take all! possible vacations)

Either way, maybe find some time to talk with a proper counselor/therapist (and not HN...). Doesn't hurt and can help with the disconnected feel.

ps. funding env for form FANG, it's good assuming you are doing something sort of close to what you were responsible for. Don't expect risk-reward to be favorable though..