Most everything I've read about L-tyrosine suggests that it may be useful in promoting alertness and focus in sleep-deprived individuals, but I'm getting the opposite result. I've noticed that if I take 1g mid-morning, I'll become irresistably sleepy after lunch. Likewise, if I take 1g before bed, I'll sleep for longer stretches of time (typically 5-6 hours at the start) and get a subjectively better quality of sleep. If I don't take any l-tyrosine, I won't get sleepy during the day, but at night I'll have more fragmented sleep; I'll typically wake every hour or two and not feel as refreshed in the morning. If I continue to abstain from taking l-tyrosine, sleep will stay fragmented, but I'll be awake longer between fragments.. and the pattern continues until I become insomnic, then alternate between insomnia and hypersomnia (unrefreshing), then I'll begin to have difficulties with cognition, mood becomes unstable, motivation disappears, I'll have episodes of dp/dr, anxiety, and suicidal thoughts that just appear out of nowhere.
My question is, why does tyrosine help me sleep and get more out of sleep? Would it be thyroid-related? Would it more likely have to do with domaminergic regulation of sleep/wake states? Any other ideas?