Time of Day?

I clearly have blood sugar 'crashes' that are precipitous and most annoying (not just for me but also for the husband who bears the burden of the rage, swoon and/or tears accompanying the event). The odd thing about them is that they typically only occur at one time of day, late afternoon.

While I can get up in the morning, eat nothing and do 60 minutes of intense aerobic exercise with no problems, 15 minutes of walking will pretty much guarantee a crash if I do it at 4:30 in the afternoon.

Essentially, even if I eat a small snack before, I have a very difficult time exercising in the late afternoon.

If I crash, I feel lousy for the rest of the day. Further, they cause me to over eat both as a preventitive measure and as a reaction to having 'crashed'.

Is it common to have a particular time of day when you are most vulnerable? Any suggestions, other than eating dinner at 4:00 for avoiding this?

Thanks,
flygirl