Old post, but this used to happen to me and still does sometimes, particularly in the summer.
Water really does help. Drink a big glass of water in the morning before coffee, and keep your Shabbos nap limited to 45 min.-1 hour. This helps me.
oomis, thank you for sharing that.
I would say even when I am depressed, looking forward to Shabbos morning keeps me going: Torah study class with the rov and getting to daven with a friendly minyan. Sometimes it’s the only time I smile all week. B”H for that.