Good for you for being on the lookout for sub drop and asking for the best ways to help! For those that don't know, sub drop can happen after an intense session, or series of sessions. All of those happy hormones flood your body, and you feel amazing... Then after some time, hours or days, your body metabolizes all those hormones and you crash. You're left feeling... Stressed or anxious or unhappy, and you probably don't even recognize what is happening. It might be mild, or it can be pretty strong. There are also physical responses in our bodies because of these hormones flooding and then depleting... You might be extra sleepy, or you might be cold. It isn't depression, but it can sometimes look a little like it.
As far as what you can do to care for your partner, aftercare immediately after is great, but even if you can't be there in person in the days after to offer physical support like hugs and orgasms �� I can tell you that for me I need extra verbal reassurance that my ler is still interested in me, that the session was as good for them as it was for me, that they want to do it again. And planning the next session can go a long way towards getting over some of my anxiety that the hormone crash has let creep in. I would make sure that you are very available to your partner in the coming days. Call or text and check in on them a little more than normal. It probably won't be this big obvious shift that you'll notice in the other person, but being flexible and supportive like you are is the best thing you can do!