I'm in a similar situation. Diagnosed MDD/PTSD..got worse when I retired from the Army. I don't get to excited for much..when it comes to racing going into it I'm, "Meh...here we go", but once I knock out those first few strokes when the gun goes off, it all comes back.

I generally use visualization more than a pump up. I made the switch mid-way through the season last year and found that my times went down (although training probably helped as well).

My old routine would be to listen to some pump up music (Fatboy Slim - Right Here, Right Now was a favorite), jump around, swing my arms to get the nerves out

Now I'll spend a few minutes meditating after doing my warm up, think about what needs to be done, go over my general game plan, and then approach the race with a more calm collected head.
I also found this works better for longer races, where you generally need to dig deep towards the latter part of the race and pace myself initially, rather than an all out effort from the get go.

No medication here, but we've all had our share of ups and downs.
Hope this helps.

Hope the meds are helping the underlying issue.

For me, race mode really begins the night before. If I lay my stuff out, plan my course, and think about what I want to do during the workout / race, before I go to bed, I wake up pretty ready to go. This is easier for a weekend workout than a workout you are trying to squeeze in on a work morning. If we are talking an actual race, than it should be on a weekend. I might even go so far as so run through a checklist for race day so I am wrapping my head around the details, and then definitely time myself if it is a workout.

Personally, though, if you are talking about trying to get into "race mode" for a workout, I never get the same rush as I get on race day morning when I see the other competitors and hear the announcer. That is something you can really only get on race day. Given how poorly I usually sleep the night before a real race, I need that rush to really get going.

What do you mean "race mode"?

I think it is best to stay calm before a race. Your routine has to e specific to your needs. I never think I am ready. I always think I haven't done enough and think I'm going to struggle to just finish. So, I've found that repeating phrases to myself before the race helps calm me down so I don't worry. I'll say thing like; "You trained for this." "You are going to swim fast."

It sounds stupid, but it seems to help me out. Last race, I started nice and calm, knowing that I was prepared. I let all the training take over and my body did what I trained it to do without my mind getting in the way by telling me I am not good enough or by getting intimidated by the other athletes.

Find a place away from all the pre-race types who want to chat it up and go over my race strategy. Most people aren't there to race.

 I visualize my race and remind myself of my strategy. I want to remind myself it’s a long day and to attempt to stick to me plan. That’s mainly for half and full distance. For sprints, I still visualize but mostly the swim start and remind myself there will be pain but it will be over fast