Hi
@LornaFarrell, You are not the first and will not be the last to do this!! We had a Prime Minister in Australia here who said "life wasn't meant to be easy". ( and later there was a scandal when he somehow lost his trousers on a train trip )!
We live and learn. To add to the excellent suggestions above I would suggest you contact your DSN when possible, explain what happen again and discuss a plan for if it should happen again. Just as we all should have sick day plans etc.
Some insulin pens have devices on them that tell you whether you have already taken a dose (so that you do not double up - and guess who has done that? yes - me).
Whether set an alarm on your watch or mobile to remind you that the Lantus dose is due, with a follow-up alarm or have some other method is up to you. Also ensure that you have a 'hospital' pack with things to take along with spare pens. glucose monitor, something to eat, drink etc. The 'alarm' could have gone off when you were at the hospital but if you don't have your insulin with you - ain't much help. Being prepared is a full time job, let alone children, husband, dog, cat .....
The important thing it that you have learnt something !!