When feeling overwhelmed, it’s tempting to respond by working harder. But humans are "cyclical" so working more doesn’t just make you miserable, it makes for worse work too.
First, give yourself permission to ease up. Don’t add unnecessary pressure by trying to "motivate yourself", which really just means beating yourself up for feeling bad.
Second, respond correctly by taking productive action and focus on pacing yourself. Re-introduce rhythm to your routine, start small, one action at a time.