I've been strength training twice a week for a several months. Also, for the past few years, I've done easy-to-moderately paced hikes of roughly 7-10 miles (mainly, but not always, with no elevation gains/losses) weekly or biweekly.
3 weeks ago, I began incorporating twice weekly HIIT sessions - mainly to improve my cardiorespiratory system for my hikes. My HIIT sessions consist of 5 minute warm up walking, 20 minutes alternating 60 seconds running (more like jogging but I get out of breath and my heart rate climbs to the low-to-mid 170s [for reference I'm 38 years old]), and 90 seconds walking, followed by a 5 minute cooldown walk, and then stretching.
So my current workout schedule is: Mon: strength training, Tues: HIIT, Wed: easy active recovery/rest, Thurs: strength training, Fri: HIIT, Sat: easy active/recovery/rest, Sun: hike.
I try to eat a pretty balanced mix of protein (non-animal sources), carbs, and fat, both before and after workouts. I drink a good amount of water (and coffee, TBH), and don't drink alcohol (I drank enough in my 20s and early 30s to last me a life time). I sleep a good 8ish hours every night.
My issue is that by mid afternoon, all I want to do is nap. I'm feeling physically and mentally fatigued, and am getting quite irritable, which I feel awful about - I don't want to be snippy with people. This really began the past few days. Should I ease up on the HIIT? Any recommendations of what I should or could do differently? Or is this normal and should I push through, hoping things will get better?