Hi N-J-C!
I don't use Levemir myself, but several others on the forum do and many find that it lasts about 18 hours rather than 24, so it might well have worn off before you have your evening snack. You might find that splitting the dose and taking some in the morning and some in the evening 12 hours apart helps, but obviously speak with your diabetes team before you try this. If you do split the dose, be aware that it will mean for some periods of the day you have one active dose working and for other periods you have two active doses working, so you might need to adjust your Novorapid ratio to account for this. Many of us do split the basal dose so it is a fairly common thing to do.
Are you carb counting to work out how much Novorapid you need? You normally count the carbs in your meal and inject the Novorapid according to whatever ratio you are. So, for someone with a 1 unit Novorapid to 10g carb (the common ratio to start on), a 40g carb meal would mean injecting 4 units Novorapid; a 50g carb meal would mean 5 units and so on. You can also get Novorapid pens with half units on them, so you could try 4.5 units which might avoid your hypo/high problems. Speak to your DSN about getting a pen with half units.
Smidge