One phrase I've found useful in similar situations was talking about "health concerns" - as opposed to "personal matters", which your friends were clearly taking badly as an explanation.
If you mention your reduced activity was due to health concerns, this should frame your choices in a way that lets them know you were unable to fulfill their expectations, that is, interact with them more during that time, even if you would have liked to. Health concerns can also be rather private, and something even friends and family are really less able to help with than specialists (doctors, etc), so it may emphasize that not telling them, and not interacting with them for a while, wasn't about excluding them from your life or not trusting them with personal information (even if it was, just a little bit).
If someone presses for further details of these health concerns, you can give whatever specific symptoms you had and feel comfortable talking about (low energy, fatigue and lethargy, stiff or achy, difficulty concentrating, difficulty sleeping, headaches, etc), or talk about the things that have helped (getting more sunlight, balanced meals, meditation, exercise, whatever did help you), or even something about any doctor's suggestions or search for a specialist (if you have something safe to share) - you don't have to give the diagnosis of "depression" as the underlying cause until or unless you trust them with that. Being able to talk about those things means that you can shy away from other topics, like diagnosis or what your doctor said about it, without making the topic stand out as that thing you don't talk about.
Depending on your relationship with the person and the conversation, you could even toss in snippets like technical biochemical symptoms ("low seratonin", "catecholamine systems, norepinephrine and dopamine, for reward processing and attention" "glutemate sensitization") to further explain while emphasizing medical symptoms rather than psychological ones.
As for the cultural belief that depression equals crazy, that can kinda work with you if you're going this route... you aren't crazy, so it will be easier for them to swallow "biochemical imbalance" or other medical symptoms without jumping to the term depression (and its cultural baggage), because you don't fit that stereotype.