If you are conscious, not nauseous and can wait twenty minutes for the pills to kick in, swallow your pills. Take an emergency dose of 100 mg of hydrocortisone or even more. Some of the effectiveness of hydrocortisone is lost when you digest it and process it to go from oral to the blood.
Injecting cortisol, especially if you do it regularly, can lead to avascular necrosis of the hip and shoulder joints. If it's unnecessary to inject steroids, don't.
If you need hydrocortisone quickly and you are not nauseous, put the pills under your tongue and let them dissolve. This is called taking hydrocortisone sublingually. The hydrocortisone will get into your bloodstream quickly. Rinse your mouth and brush your teeth to avoid getting thrush of the mouth.
If you are nauseous, have vomited twice, feel faint, have dangerously low blood pressure, have been in an accident, are losing blood or have had an emergency, give yourself (or have someone else) give you the damned shot.
Realistically, what are the risks of injecting 100 mg Solu-Cortef? Your blood sugar might go high. You can and have done that by drinking soda*. You might be a little jittery. You might get irritable. I can guaranty you that if you think you need a shot and did it, you were irritable in the first place. No one (except Drama Queens and people with Munchhausen's) injects for fun. If you feel like you're in a bad enough place to consider a shot, just do it. You don't want to end up dead.
Let's get back to taking hydrocortisone (HC) orally. I think many of us, myself included, try to hold out on taking extra HC when we're not feeling well. There's that guilt factor of "what if I'm taking too much" as well as the stupid brainfog which makes you think, "Oh, it's not so bad." These are very stupid reasons for not taking enough HC when you need it. If you think either of these stupid thoughts while simultaneously thinking about whether you should take more HC. Go get the HC and take 10 mg. If it's too much, skip, delay or make your next dose smaller.
What is the #1 risk of a crisis? Death. Death is irreversible. What can keep you from a crisis? Hydrocortisone or Solu-Cortef. If you take too much, it will be more or less out of your system in eight hours. Cortisol dosing is flexible. You can make mistakes and learn from them. You can make changes from minute to minute and day to day.
Be kind to your body. Give it the raw materials it needs to keep you from crisis. Don't skimp on cortisol because you're not sure if you're sick enough for more.
*Dave, you said "big slab of chocolate cake"