The worst part for me with ITP is that not knowing if its an innocent bruise or an ITP bruise..... Or in other words, when to ring and when to manage.
Hope you do ring up though because even if not dropped that low they would like to know. But you are now in your 50's and you haven't had it since high school you say? wow that is a long time. What was treatment like in those days? It may well have moved on and certainly the environment has. Please, please please, if you have open access to the ward, give them a ring now:-} if not go and see your doc as soon as possible because the sooner you report it, then the quicker you mend per se.
It be interesting to hear how you were treated with it when you were a teen? And if it is any different to now.