ok i have the same problem some days. it almost always has to do with my morning. if i jump out of bed as soon as my alarm rings all happy and excited, my day is great. if i turn off the alarm and stay in bed for a few more minutes or fall back asleep, my day turns out slow. like you said, when my day starts slow the rest of my day just suffers from it. and i learned that your mindset and mood for the rest of the day pretty much depends on your morning, at least for me. did you have a slower than usual morning? you might want to start there.
one little problem to overcome is this thing called 'sleep inertia'. its the feeling you always get when you wake up in the morning and you just feel too tired to get up. youre dont actually need more sleep, but your body just wants to go back to sleep, or something. its especially effective during the winter, where its still completely dark in the morning or when theres just really nothing important going on in the day. this just takes sheer willpower to overcome. you might try to convince yourself that a few more minutes wouldnt hurt, but believe me ignore that. if youre really unlucky, you might even go back to sleep. tell yourself that the quicker you get up the better your day will be, that the sleep inertia will fade away quickly (it always does), force yourself to get up, whatever. in 5 minutes you wont even be tired anymore and you'll have more time in the morning and you'll be glad you made yourself get up promptly. youll be energized and in the right 'mindset' and mood.
i dont know if this is your problem, but it was mine and helped me a lot. just remember to not start your day slow, like you said, you will thank yourself later in the day, when your not suffering from lack of concentration and energy.